Apparatus And Method For Testing Defects

ABSTRACT

An apparatus and method for detecting defects on a specimen includes an illumination optical unit which obliquely projects a laser focused onto a line on a surface of the specimen, a table unit which mounts the specimen and which is movable, a detection optical unit which detects with an image sensor an image of light formed by light reflected from the specimen and passed through a filter which blocks diffraction light resulting from patterns formed on the specimen, a signal processor which processes a signal outputted from the image sensor of the detection optical unit to extract defects of the specimen, and a display unit which displays information of defects extracted by the signal processor. The filter is adjustable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 11/681,981, filed Mar. 5, 2007, which is a divisional application ofU.S. application Ser. No. 11/244,080, filed Oct. 6, 2005, which is acontinuation of U.S. application Ser. No. 10/170,378, filed Jun. 14,2002, now U.S. Pat. No. 7,037,735, which is a continuation of U.S.application Ser. No. 09/362,135, filed Jul. 28, 1999, now U.S. Pat. No.6,411,377, which is a continuation-in-part of U.S. application Ser. No.08/535,577, filed Sep. 28, 1995, which is a continuation application ofU.S. application Ser. No. 08/046,720, filed Apr. 16, 1993, now U.S. Pat.No. 5,463,459, which is a continuation-in-part of U.S. application Ser.No. 07/679,317, filed Apr. 2, 1991, now U.S. Pat. No. 5,233,191 and U.S.application Ser. No. 07/778,363, filed Oct. 17, 1991, now U.S. Pat. No.5,274,434, the subject matter thereof being incorporated by referenceherein. This application also relates to U.S. application Ser. No.11/244,078, filed on Oct. 6, 2005, now U.S. Pat. No. 7,098,055, which isa divisional application of U.S. application Ser. No. 10/170,378, filedJun. 14, 2002, now U.S. Pat. No. 7,037,735. This application relates toU.S. application Ser. No. 11/681,996, filed on Mar. 5, 2007, now U.S.Pat. No. 7,443,496, which is a continuation application of U.S.application Ser. No. 11/244,080, filed Oct. 6, 2005.

BACKGROUND OF THE INVENTION

The present invention relates to a defect testing apparatus and a defecttesting method for inspecting a state of generation of defects such asforeign particles in a fabrication process such as a semiconductorfabrication process, a liquid-crystal-display fabrication process and aprint-board fabrication process wherein a defect such as a foreignparticle generated in a process to create a pattern on a substrate toproduce an object is detected and analyzed in order to determine acountermeasure.

In the conventional semiconductor fabrication method, a foreign particleexisting on a semiconductor substrate also known as a wafer causes adefect such as poor insulation of a wire or a short circuit.Furthermore, in the case of a miniaturized semiconductor device, aninfinitesimal foreign particle existing in a semiconductor substrateresults in poor insulation of a capacitor or destruction of typically agate oxide film. These foreign particles are introduced to get mixedwith a semiconductor material in a variety of states due to a variety ofcauses. For example, a foreign particle is generated by a movable partof a transportation apparatus or a human body. A foreign particle canalso be generated as a result of a chemical reaction in processingequipment using a process gas or mixed with chemicals or a raw material.

Likewise, if a foreign particle is introduced to get mixed with apattern, causing some defects in a process to fabricate a liquid-crystaldisplay device, the resulting display device is not usable. The processto fabricate a print board is in the same situation, That is to say, amixed foreign particle causes a poor connection and a short circuit in apattern.

One of publications for detecting a foreign particle on a semiconductorsubstrate of this type is disclosed in Japanese Patent Laid-open No. Sho62-89336 and referred to hereafter as publication 1. According to thisprior art, a laser beam is radiated to a semiconductor substrate. If aforeign particle is stuck to the semiconductor substrate, the foreignparticle will generate scattered beams which can then be detected andcompared with a result of inspection for a semiconductor substrate ofthe same type inspected immediately before. In this way, a difference ininspection result can be detected and used to eliminate a patterndefect. As a result, a foreign particle and a defect can be detectedwith a high degree of sensitivity and a high degree of reliability.Another publication referred to hereafter as publication 2 is disclosedin Japanese Patent Laid-open No. Sho 63-135848. According to thispublication, a laser beam is radiated to a semiconductor substrate. If aforeign particle is stuck to the semiconductor substrate, the foreignparticle will generate scattered beams which can then be detected. Adetected beam generated by a foreign particle is analyzed by using ananalysis technique such as laser photo luminescence or a secondary X-rayanalysis (XMR).

In addition, as a technology for detecting a foreign particle, there isalso known a technique whereby a coherent beam is radiated to a wafer,and the beam reflected by repetitive patterns on the wafer is removed byabout a spatial filter to emphasize light components generated by aforeign particle or a defect which does not exhibit repetitiveness. Inthis way, a foreign particle or a defect can be detected.

A technology disclosed in Japanese Patent Laid-open No. Hei 1-117024 isreferred to hereafter as publication 3. According to this publication,in a foreign particle inspecting apparatus, a beam is radiated to acircuit pattern on a wafer in a direction forming an angle of 45 degreeswith respect to a group of main straight lines of the circuit patternand a 0th-order diffracted beam from the group of main straight lines isintroduced into the aperture of an objective lens. The disclosure alsoincludes a description which states that, according to publication 3, abeam from any group of straight lines other than the group of mainstraight lines is shielded by a spatial filter.

In addition, other publications related to apparatuses and methods fordetecting defects such as foreign particles are disclosed in JapanesePatent Laid-open No. Hei 1-250847, Japanese Patent Laid-open No. Hei6-258239, Japanese Patent Laid-open No. Hei 6-324003, Japanese PatentLaid-open No. Hei 8-210989 and Japanese Patent Laid-open No. Hei8-271437 and referred to as publications 4, 5, 6, 7 and 8 respectively.With publications 1 to 8 mentioned above, however, it is impossible todetect a defect such as an infinitesimal foreign particle on asubstrate, on which repetitive patterns coexist with non-repetitivepatterns, at a high speed, with ease and with a high degree ofsensitivity.

To put it in detail, publications 1 to 8 have a problem of asubstantially reduced sensitivity (increased minimum dimensions of adetected foreign particle) in the case of a part of the substrate otherthan the repetitive portion such as memory cells.

In addition, publications 1 to 8 also have a problem of a substantiallyreduced sensitivity in the case of an oxide film which passes aradiation beam.

Moreover, publications 1 to 8 also have a problem of inability to detecta defect such as an infinitesimal foreign particle.

Furthermore, in the case of publications 1 to 8, a mass-productionbuild-up line or a pilot line and a mass-production line of asemiconductor production process are not distinguished from each other.That is to say, inspection equipment used in the mass-productionbuild-up work is also used in a mass-production line without change inspite of the fact that it is necessary to early detect generation of aforeign particle on the mass-production line and determine acountermeasure for the detected foreign particle.

At any rate, the conventional defect inspecting apparatus is large insize and has such a configuration that the apparatus must be installedindependently. For this reason, in order to inspect a foreign particleand a defect, it is necessary to transport a semiconductor substrate, aliquid-crystal-display substrate or a print substrate which has beenprocessed along the mass-production line to a place at which the defectinspecting apparatus is installed. That is to say, it takes time totransport the substrate and to inspect the substrate for a foreignparticle and a defect. As a result, complete inspection is difficult. Inaddition, it is hard to carry out such sampling inspection at asufficiently high frequency.

Further, a defect inspecting apparatus with such a configurationrequires an operator.

SUMMARY OF THE INVENTION

It is thus an object of the present invention addressing the problemsdescribed above to provide a defect inspecting apparatus and a defectinspection method capable of inspecting a defect such as aninfinitesimal foreign particle on an inspected substrate containingrepetitive patterns, non-repetitive patterns and non-patterns whichcoexist with each other at a high speed and with a high degree ofprecision.

It is another object of the present invention to provide a defectinspecting apparatus and a defect inspection method which allow ahigh-efficiency substrate fabrication line to be constructed byimplementation of complete inspection and sampling inspection at asufficiently high frequency.

It is still another object of the present invention to provide a defectinspecting apparatus and a defect inspection method which are capable ofinspecting also a defect such as an extremely infinitesimal foreignparticle having a size of the order of 0.1 μm or smaller at a high speedand with a high degree of sensitivity by effectively utilizing the lightquantity of a Gaussian beam generated by an ordinary inexpensive lightsource such as a laser-beam source.

It is a further object of the present invention to provide a defectinspecting apparatus and a defect inspection method which are capable ofinspecting also a defect such as an extremely infinitesimal foreignparticle having a size of the order of 0.1 μm or smaller at a high speedand with a high degree of sensitivity by effectively utilizing the lightquantity of a Gaussian beam generated by typically a laser-beam sourceand by resolving a problem of a lack of illumination at regionssurrounding an area on a substrate being inspected due to a decrease inMTF at locations separated away from an optical axis in a detectionoptical system.

It is a still further object of the present invention to provide adefect inspecting apparatus capable of inspecting a defect such as areal foreign particle by setting the level of a threshold value at aproper degree of sensitivity without substantially increasing the amountof generated false information wherein the threshold value is used as acriterion as to whether or not a defect exists in a variety ofcircuit-pattern areas in the device structure laid out on a substratebeing inspected.

It is a still further object of the present invention to provide adefect inspecting apparatus capable of inspecting a defect such as aforeign particle with a specified size to be detected by setting thelevel of a threshold value used as a criterion as to whether or not adefect exists for the size of the defect to be detected in a variety ofcircuit-pattern areas in the device structure laid out on a substratebeing inspected.

It is a still further object of the present invention to provide adefect inspecting apparatus capable of inspecting a defect such as aforeign particle by allowing the size of the defect existing in avariety of circuit-pattern areas in the device structure laid out on asubstrate being inspected to be inferred.

It is a still further object of the present invention to provide asemiconductor-substrate fabricating method for fabricating asemiconductor substrate at a high efficiency and, hence, at a highyield.

In order to achieve the objects described above, the present inventionprovides a defect inspecting apparatus and a defect inspection methodadopted by the defect inspecting apparatus comprising: a stage formounting and moving an inspected substrate with a circuit patterncreated thereon; an illumination optical system for illuminating thesubstrate by forming a beam radiated by a light source into aslit-shaped beam and directing the beam toward the substrate beinginspected at a predetermined gradient of (π/2−α1) with respect to thedirection of a line normal to the substrate and a predetermined gradientof ΦI with respect to a group of main straight lines of the circuitpattern on the surface of the substrate wherein the longitudinaldirection is almost perpendicular to a direction of the y axis of themovement of the stage; a detection optical system including an imagesensor for receiving scattered beams reflected by a defect such as aforeign particle existing on the inspected substrate illuminated by theslit-shaped beam radiated by the illumination optical system and forconverting the scattered beams into a detection signal representing aresult of detection of the defect; and an image-signal processing unitfor extracting a signal showing the defect such as a foreign particle onthe basis of the detection signal output by the image sensor employed inthe detection optical system.

In addition, in order to achieve the objects described above, thepresent invention also provides a defect inspecting apparatus and adefect inspection method adopted by the defect inspecting apparatuscomprising: a stage for mounting and moving an inspected substrate withcircuit patterns created thereon; an illumination optical system forilluminating the substrate by forming a beam radiated by a light sourceinto a slit-shaped beam and directing the beam toward the substratebeing inspected at a predetermined gradient of (π/2−α1) with respect tothe direction of a line normal to the substrate and a predeterminedgradient of with respect to a group of main straight lines of thecircuit pattern on the surface of the substrate wherein the longitudinaldirection is almost perpendicular to a direction of the y axis of themovement of the stage; a detection optical system including an imagesensor for receiving scattered beams reflected by a defect such as aforeign particle existing on the inspected substrate illuminated by theslit-shaped beam radiated by the illumination optical system and forconverting the scattered beams into a detection signal representing aresult of detection of the defect; and an image processing unit having:a criterion setting means which calculates a variation of the detectionsignal output by the image sensor of the detection optical system torepresent a variation of a scattered beam reflected by areas on thesurface of the substrate in which the naturally identical circuitpatterns are created or regions in close proximity to the areas andwhich sets a criterion (threshold value) based on the calculatedvariation; and a signal extracting means which extracts a signal showingthe defect such as a foreign particle from the detection signal outputby the image sensor employed in the detection optical system on thebasis of the criterion set by the criterion setting means.

Furthermore, the present invention also provides a defect inspectingapparatus and a defect inspection method adopted by the defectinspecting apparatus comprising: a stage unit for mounting and moving aninspected substrate with a circuit pattern created thereon; anillumination optical system for illuminating the substrate by forming abeam radiated by a light source into a slit-shaped beam and directingthe beam toward the substrate being inspected at a predeterminedgradient with respect to the direction of a line normal to the substrateand a predetermined gradient with respect to a group of main straightlines of the circuit pattern on the surface of the substrate wherein thelongitudinal direction is almost perpendicular to a y direction of themovement of the stage; a detection optical system including an imagesensor for receiving scattered beams reflected by a defect such as aforeign particle existing on the inspected substrate illuminated by theslit-shaped beam radiated by the illumination optical system and forconverting the scattered beams into a detection signal representing aresult of detection of the defect; and an image-signal processing unitfor extracting a signal showing the defect such as a foreign particlefrom the detection signal output by the image sensor employed in thedetection optical system on the basis of a criterion (threshold value)set for each of a variety of areas composing the circuit pattern.

Moreover, in the defect inspecting apparatuses and the defect inspectionmethods provided by the present invention, the predetermined gradient ofΦI of the slit-shaped beams with respect to a group of main straightlines of the circuit pattern on the surface of the substrate is about 45degrees.

Further, in the defect inspecting apparatuses and the defect inspectionmethods provided by the present invention, the optical axis of thedetection optical system is substantially perpendicular to the substratebeing inspected.

In addition, in the defect inspecting apparatuses and the defectinspection methods provided by the present invention, the optical axisof the detection optical system is inclined with respect to the linenormal to the substrate being inspected.

Furthermore, in the defect inspecting apparatus provided by the presentinvention, the light source employed in the illumination optical systemis a laser-beam source.

Moreover, in the defect inspecting apparatus provided by the presentinvention, the illumination optical system has an optical element of ashape resembling a cone for generating a converged light.

Further, in the defect inspecting apparatus provided by the presentinvention, the illumination optical system is provided with an opticalsystem for radiating a white light in a direction inclined with respectto a normal line to a substrate being inspected.

In addition, in the defect inspecting apparatus provided by the presentinvention, the illumination optical system is provided with a spacefilter.

Furthermore, in the defect inspecting apparatus provided by the presentinvention, the image sensor employed in the detection optical system isa TDI (Time Delay Integration) image sensor.

Moreover, the present invention provides a defect inspecting apparatuscomprising: an illumination optical system having an optical element ofa shape resembling a cone for radiating an illumination light beam in adirection at a predetermined gradient with respect to a line normal tothe surface of an object of inspection and for converging theillumination light beam in at least one direction on the surface of theobject of inspection; a detection optical system including an imagesensor which receives a light reflected by the object of inspection andconverts the received light into a detection signal; and an image-signalprocessing unit for processing the detection signal output by thedetection optical system.

Further, the detection optical system employed in the defect inspectingapparatus provided by the present invention has: a beam splittingoptical system for splitting a light beam reflected by the object ofinspection into reflected beams with one of the reflected beams havingan intensity of about 1/100 of that of another; and a plurality of imagesensors for receiving each of the reflected beams split by the beamsplitting optical system.

In addition, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of circuit patterns with substantially identical shapes arelaid out; a detection optical system including an image sensor forreceiving a light reflected by the object of inspection and forconverting the received light into a detected image signal; and animage-signal processing unit for processing the detected image signaland being provided with: a criterion setting means which calculates avariation of an image signal among pixels which correspond to thecircuit patterns with identical shapes or pixels in close proximitythereto on the basis of the image signal detected by the detectionoptical system and which sets a threshold value to serve as a criterionas to whether or not a defect such as a foreign particle exists on thebasis of the calculated variation of the image signal; and a judgmentmeans which forms a judgment as to whether or not a defect exists fromthe image signal detected by the detection optical system on the basisof the criterion set by the criterion setting means.

Furthermore, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of patterns with substantially identical shapes are laid out;a detection optical system including an image sensor for receiving alight reflected by the object of inspection and for converting thereceived light into a detected image signal; and an image-signalprocessing unit for processing the detected image signal and beingprovided with: a difference computing means which computes differencesin image signal among pixels corresponding to the patterns havingidentical shapes on the basis of an image signal detected by thedetection optical system; a criterion setting means which calculates avariation of the differences computed by the difference computing meansat a plurality of for pixels adjacent to pixels used for forming ajudgment as to whether or not a defect such as a foreign particle existsand which sets a criterion of the level of a pixel signal used fordetermining whether or not the defect such as the foreign particleexists on the basis of the calculated variation; and a judgment meanswhich forms a judgment as to whether or not the defect exists from theimage signal detected by the detection optical system on the basis ofthe criterion set by the criterion setting means.

Moreover, in the defect inspecting apparatus provided by the presentinvention, the image-signal processing unit has an output means whichoutputs pieces of a result of defect inspection produced by the judgmentmeans and data representing the criterion set by the criterion settingmeans.

Further, the present invention provides a defect inspecting apparatuscomprising: an illumination optical system for radiating an illuminationlight to a surface of an object of inspection on which a plurality ofpatterns with substantially identical shapes are laid out; a detectionoptical system including an image sensor for receiving a light reflectedby the object of inspection and for converting the received light into adetected image signal; and an image-signal processing unit having: ajudgment means which forms a judgment as to whether or not a defectexists by comparison of the image signal output by the detection opticalsystem with a criterion; and a display means which displays mapinformation or images on the patterns having identical shapes to be usedas the criterion by the judgment means, or which displays relationsbetween criteria (or sensitivities) and indicators of inspection areafor them, or which displays sensitivity information on circuit patternshaving identical shapes corresponding to criteria.

In addition, the image-signal processing unit employed in the defectinspecting apparatus provided by the present invention has an areapriority mode, a standard mode and a sensitivity priority mode ascondition specifying modes.

Furthermore, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection on which aplurality of patterns with substantially identical shapes are laid out;a detection optical system including an image sensor for receiving alight reflected by the object of inspection and for converting thereceived light into a detected image signal; and an image-signalprocessing unit for processing the detected image signal and beingprovided with: a criterion setting means which sets a criterion byvarying the criterion in accordance with a state of an underlying layerin the patterns with identical shapes; and a judgment means which formsa judgment as to whether or not a defect exists by comparison of theimage signal output by the detection optical system with the criterionset by the criterion setting means.

Moreover, the present invention provides a defect inspecting apparatuscomprising: an illumination optical system for radiating an illuminationlight to a surface of an object of inspection on which a plurality ofpatterns with substantially identical shapes are laid out; a detectionoptical system including an image sensor for receiving a light reflectedby the object of inspection and for converting the received light into adetected image signal; and an image-signal processing unit forprocessing the detected image signal output by the detection opticalsystem and being provided with: a size specifying means which specifiesa size of a defect; a criterion setting means which sets a criterion byvarying the criterion in accordance with the defect size specified bythe size specifying means; and a judgment means which forms a judgmentas to whether or not a defect exists by comparison of the image signaloutput by the detection optical system with the criterion set by thecriterion setting means.

Further, the present invention provides a defect inspecting apparatuscomprising: an illumination optical system for radiating an illuminationlight to a surface of an object of inspection on which a plurality ofpatterns with substantially identical shapes are laid out; a detectionoptical system including an image sensor for receiving a light reflectedby the object of inspection and for converting the received light into adetected image signal; and an image-signal processing unit forprocessing the detected image signal output by the detection opticalsystem and being provided with: a size specifying means which specifiesa size of a defect; and a control means which controls the power of theillumination light radiated by the illumination optical system inaccordance with the defect size specified by the size specifying means.

In addition, the present invention provides a defect inspectingapparatus comprising: an image-pickup optical system having: anillumination optical subsystem for radiating an illumination light to asurface of an object of inspection mounted on a stage with the objecthaving a plurality of patterns having substantially identical shapeslaid out on the object of inspection; and a detection optical subsystemincluding an image sensor for receiving a light reflected by the objectof inspection and for converting the received light into a detectedimage signal; an image-signal processing unit including a judgment meanswhich forms a judgment as to whether or not a defect exists bycomparison of the image signal output by the detection optical subsystememployed in the image-pickup optical system with a criterion; and anoptical observation microscope provided along with the image-pickupoptical system and used for observation of an optical object on theobject of inspection.

Furthermore, in the defect inspecting apparatus provided by the presentinvention, the optical observation microscope is implemented by anultraviolet-ray optical observation microscope.

Moreover, the present invention provides a defect inspecting apparatuscomprising: an illumination optical system for radiating an illuminationlight to a surface of an object of inspection; a detection opticalsystem including a photo-electrical conversion means which receives alight reflected by the object of inspection and converts the receivedlight into a detected signal; and an image-signal processing unitincluding a means which detects a defect by processing the signaldetected by the detection optical system and outputs a result of thedefect detection including pattern information indicating existence of adefect.

Further, in the defect inspecting apparatus provided by the presentinvention, the pattern information output by the means employed in theimage-signal processing unit is information obtained from design data ofpatterns.

In addition, the present invention provides a defect inspectingapparatus comprising: an illumination optical system for radiating anillumination light to a surface of an object of inspection; a detectionoptical system including a photo-electrical conversion means whichreceives a light reflected by the object of inspection and converts thereceived light into a detected signal; and an image-signal processingunit including a means which extracts a signal level of a defect byprocessing the signal detected by the detection optical system, andwhich corrects the extracted defect signal level so as to make thesignal level indicate the size of the defect, and which outputs thecorrected defect signal level.

Furthermore, the means employed in the image-signal processing unit ofthe defect inspecting apparatus provided by the present inventioncorrects the signal level of the defect on the basis of the intensity ofthe illumination light or data representing the reflectance of thesurface of a pattern.

Moreover, the illumination optical system employed in the defectinspecting apparatus provided by the present invention is configured sothat a light source thereof radiates a slit-shaped beam to a detectionarea on a substrate serving as an object of inspection wherein theslit-shaped beam is formed into a slit-shaped Gaussian beam exhibiting aGaussian illumination distribution having a standard deviationsubstantially equal to a distance from an optical axis of the detectionarea to a periphery.

Further, the illumination optical system employed in the defectinspecting apparatus provided by the present invention is configured tohave a light source thereof radiate a slit-shaped beam to a detectionarea on a substrate serving as an object of inspection wherein theslit-shaped beam is formed into a slit-shaped Gaussian beam by properlyadjusting a diameter or a major-axis length of the beam to a distancebetween peripheries having the center thereof coinciding with an opticalaxis of the detection area so that a ratio of an illumination at theperipheries of the detection area to an illumination at the center ofthe detection area has a value in the range 0.46 to 0.73.

In addition, in the defect inspecting apparatus provided by the presentinvention, the slit-shaped Gaussian beam radiated by the illuminationoptical system is a DUV (Deep Ultra-Violet) beam.

In the configurations described above, it is possible to detect a defectsuch as an infinitesimal foreign particle on an inspected substrate, onwhich repetitive patterns, non-repetitive patterns and non-patternscoexist with each other, at a high speed and with a high degree ofprecision.

In addition, in the configurations described above, by effectivelyutilizing the light quantity of a Gaussian beam radiated by an ordinaryinexpensive light source such as a laser-beam source, it is possible todetect also a defect such as an infinitesimal foreign particle with asize of the order of 0.1 μm or smaller at a high speed and with a highdegree of sensitivity.

Furthermore, in the configurations described above, by effectivelyutilizing the light quantity of a Gaussian beam radiated by typically alaser-beam source, it is possible to detect also a defect such as aninfinitesimal foreign particle with a size of the order of 0.1 μm orsmaller at a high speed and with a high degree of sensitivity byresolving a problem of a lack of illumination at regions surrounding anarea on a substrate being inspected due to a decrease in MTF atlocations separated away from an optical axis in a detection opticalsystem.

Moreover, in the configurations described above, it is possible todetect a defect such as a real foreign particle by setting the level ofa threshold value at a proper degree of sensitivity withoutsubstantially increasing the amount of generated false informationwherein the threshold value is used as a criterion as to whether or nota defect exists in a variety of circuit-pattern areas in the devicestructure laid out on a substrate being inspected.

Further, in the configurations described above, it is possible to detecta defect such as a foreign particle with a size to be detected bysetting the level of a threshold value used as a criterion as to whetheror not a defect exists for the size of the defect to be detected in avariety of circuit-pattern areas in the device structure laid out on asubstrate being inspected.

In addition, in the configurations described above, it is possible todetect a defect such as a foreign particle by allowing the size of thedefect existing in a variety of circuit-pattern areas in the devicestructure laid out on a substrate being inspected to be inferred.

Furthermore, in the configurations described above, it is possible toconstruct a high-efficiency substrate fabrication line by implementationof complete inspection and sampling inspection at a sufficiently highfrequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a semiconductor wafer serving as a substratewhich has memory LSIs laid thereon and is to be inspected by a defectinspecting apparatus implemented by an embodiment of the presentinvention;

FIG. 2 is a diagram showing a semiconductor wafer serving as a substratewhich has LSIs such as microcomputers laid thereon and is to beinspected by the defect inspecting apparatus implemented by anotherembodiment of the present invention;

FIG. 3 is a diagram showing the configuration of a first embodimentimplementing a defect inspecting apparatus provided by the presentinvention in a simple and plain manner;

FIG. 4 is a block diagram showing the configuration of a secondembodiment implementing an image-signal processing unit employed in thedefect inspecting apparatus shown in FIG. 3;

FIG. 5 is an explanatory diagram used for describing a method providedby the present invention to radiate a slit-shaped beam to a substratebeing inspected such as a semiconductor wafer and a method provided bythe present invention to detect a beam reflected by the substrate;

FIG. 6 is a diagram showing a squint view of a light beam radiated by anillumination lens with a conical surface provided by the presentinvention;

FIG. 7 is an explanatory diagram used for describing a first embodimentimplementing a method to manufacture an illumination lens with a conicalsurface provided by the present invention;

FIG. 8 is an explanatory diagram used for describing a second embodimentimplementing a method to manufacture an illumination lens with a conicalsurface provided by the present invention;

FIG. 9( a) is a diagram showing a side view in the direction of the yaxis of an illumination optical system provided by the present inventionand FIG. 9( b) is a diagram showing a side view in the direction of thex axis of the illumination optical system provided by the presentinvention;

FIG. 10 is a diagram showing a top view of an optical subsystem forradiating slit-shaped beams generated by a single laser-beam source in 3directions to a substrate being inspected such as a semiconductor waferin the illumination optical system provided by the present invention;

FIG. 11( a) is a diagram showing a birds eye view of radiation anddetection directions according to the present invention whereas FIG. 11(b) is a diagram showing a birds eye view of a diffraction light obtainedas a result of reflection of a light radiated in the radiation directionby a pattern;

FIG. 12 is a diagram showing a relation between: a state of generationof a 0th-order diffraction-light pattern by radiation of a slit-shapedbeam in a direction forming an angle of 45 degrees with a group of mainstraight lines of a circuit pattern according to the present invention;and an aperture of an objective lens employed in a detection opticalsystem with an optical axis thereof oriented in a vertical direction;

FIG. 13 is a diagram showing a relation between: a state of generationof a 0th-order diffraction-light pattern by radiation of a slit-shapedbeam in a direction parallel to a group of main straight lines of acircuit pattern according to the present invention; and an aperture ofan objective lens, employed in a detection optical system with anoptical axis thereof oriented in a vertical direction;

FIG. 14 is a diagram showing a relation between: slit-shaped beamsradiated in 3 different directions each forming an angle of 45 degreeswith a group of main straight lines of a circuit pattern according tothe present invention; and a detection area detected by a TDI imagesensor.

FIG. 15 is a diagram showing the configuration of a second embodimentimplementing a defect inspecting apparatus provided by the presentinvention in a simple and plain manner;

FIG. 16 is a diagram showing graphs each representing a relation betweenan angle of emission from a foreign particle and the intensity of adetection signal;

FIG. 17 is a diagram showing an embodiment wherein an optical axis of adetection optical system is inclined at a gradient and photo sensitivesurface of a TDI image sensor is inclined at a slope adjusted to thegradient;

FIG. 18 is a diagram showing a state of projection of a diffractionlight beam which is generated by a repetitive pattern when a slit-shapedbeam is radiated in a direction forming an angle of 45 degrees with agroup of main straight lines of a circuit pattern according to thepresent invention;

FIG. 19( a) is a diagram showing a top view of diffraction light beamsgenerated by repetitive patterns on a Fourier transformation plane of adetection optical system provided by the present invention; and FIG. 19(b) is a diagram showing a relation between the positions of diffractionlight beams and a spatial filter;

FIG. 20 is a diagram showing relations between: a state of generation ofa 0th-order diffraction-light pattern by radiation of a slit-shaped beamin a direction forming an angle of 45 degrees with a group of mainstraight lines of a circuit pattern according to the present invention;and an aperture of an objective lens of a detection optical system withan optical axis thereof oriented in a vertical direction and thedirection of the y axis;

FIG. 21 is a diagram showing a relation between: a state of generationof a 0th-order diffraction-light pattern by radiation of a slit-shapedbeam in a direction parallel to a group of main straight lines of acircuit pattern according to the present invention; and an aperture ofan objective lens of a detection optical system with the 0th-orderdiffraction-light pattern not getting in;

FIG. 22 is a diagram showing an embodiment of the present inventionwherein a slit-shaped beam with its longitudinal direction oriented inthe direction of radiation is radiated to a substrate in a directionforming an angle of 45 degrees with a group of main straight lines of acircuit pattern on the substrate according to the present invention;

FIG. 23 is a diagram showing a special TDI image sensor which isrequired when the slit-shaped beam shown in FIG. 22 is radiated;

FIG. 24 is a diagram showing a side view of an interference model oflights scattered by a foreign particle existing on an insulation filmsuch as an oxide film being inspected in accordance with the presentinvention;

FIG. 25 is an explanatory diagram used for describing an embodiment fordetecting lights scattered by a foreign particle existing on aninsulation film such as an oxide film in a plurality of detectiondirections in order to detect the foreign particle;

FIG. 26( a) is a diagram showing a relation between the thickness changeof an insulation film such as an oxide film and a detection signal foran illumination light having a certain wavelength; and FIG. 26( b) is adiagram showing a relation between the thickness change of an insulationfilm such as an oxide film and a detection signal for illuminationlights having 3 different wavelengths;

FIG. 27( a) is a diagram showing a relation between pixels and a waferused for explaining why it is necessary to compute and set a criterion(threshold value) for extracting a defect such as a foreign particle inan image-signal processing unit provided by the present invention; andFIG. 27( b) is a diagram showing a relation between pixels and chipswhich each have a variety of pattern areas;

FIG. 28 is a block diagram showing a first embodiment of theimage-signal processing unit provided by the present invention;

FIG. 29 is a block diagram showing a third embodiment of theimage-signal processing unit provided by the present invention;

FIG. 30 is a block diagram showing a fourth embodiment of theimage-signal processing unit provided by the present invention;

FIG. 31 is a block diagram showing a fifth embodiment of theimage-signal processing unit provided by the present invention;

FIG. 32 is a diagram showing the configuration of a semiconductorfabrication line along which apparatuses for detecting defects such asforeign particles are installed;

FIG. 33 is an explanatory diagram used for describing the fact that, byincreasing the number of various defect inspecting apparatuses which areinstalled along a semiconductor fabrication line and capable ofdetecting a variety of foreign particles, it is possible to construct asystem displaying a high performance as a whole;

FIG. 34 is a diagram showing changes in yield and defect count that areobserved during a build-up period of mass production;

FIG. 35 is a diagram showing the configuration of a fourth embodimentimplementing a defect inspecting apparatus provided by the presentinvention in a simple and plain manner;

FIG. 36( a) is a diagram showing an embodiment implementing anillumination optical system employed in the fourth embodimentimplementing a defect inspecting apparatus of FIG. 35 in concrete termsas seen from a position on the y axis; and FIG. 36( b) is a diagramshowing the same in concrete terms as seen from a position on the xaxis;

FIG. 37 is an explanatory diagram used for describing a basic concept ofshaping a slit-shaped Gaussian beam by means of an illumination opticalsystem to increase the illumination efficiency;

FIGS. 38( a) and 38(b) are explanatory diagrams used for describing animage-pickup method to receive a light representing an optical image inan area of detection on a substrate being inspected by using a TDI imagesensor as a detector;

FIG. 39 is a diagram showing variations in illumination f(x₀) at aperiphery (x₀=1) of a detection area with changes in standard deviationσ (corresponding to the width of illumination) of a Gaussian Beam;

FIG. 40 is a diagram showing variations in illumination f(x₀) withchanges in distance x₀ from the optical axis of a detection area for aradiated Gaussian beam at standard deviations σ of 0.5, 1 and 2;

FIGS. 41( a) and 41(b) are explanatory diagrams used for describing anembodiment implementing a TDI image sensor capable of receiving a DUVlight;

FIG. 42 is a diagram showing an embodiment of a sequence of conditionspecifying processes in a defect inspecting apparatus provided by thepresent invention;

FIG. 43 is a diagram showing a screen displayed on a display means andused for selecting a condition specifying mode and selecting a thresholdvalue in advance;

FIG. 44 is a diagram showing a screen appearing on a display means toshow detection sensitivities and detection areas;

FIG. 45 is a diagram showing a screen appearing on a display means toshow threshold value maps for area-priority, standard andsensitivity-priority modes as well as relations between the sensitivityand the inspection area;

FIG. 46 is a diagram showing an embodiment implementing a defectinspecting apparatus including a detection optical system having anoptical subsystem for observing a shielded-light pattern of a spatialfilter and an optical-observation microscope;

FIG. 47 is a diagram showing a relation based on empirical data betweenan evaluation value (a level of a detection signal of scattered lights)and a standard diameter of particles on a reflecting-surface wafer usedin the present invention;

FIGS. 48( a) and 48(b) are explanatory diagrams used for describing anembodiment for inferring the size of a foreign particle from a detectedimage signal;

FIG. 49 is an explanatory diagram used for describing an embodimentcapable of classifying the types of defects from the level of a signaldetected by a laser radiating system and the level of a signal detectedby another radiation system;

FIG. 50 is a diagram showing the configuration of a defect inspectingapparatus of the present invention including a detection optical systemand an illumination optical system for radiating a beam by adoption of abright visual field technique by means of a straight-line-shaped finemirror;

FIG. 51 is a diagram showing an embodiment wherein a substrate isinspected for a defect at a high sensitivity prior to processing by aprocess performing apparatus P to produce a pre-processing result A, thesurface is inspected for a defect after the processing to produce apost-processing result B and a logic difference (B−A) is found; and

FIG. 52 is a diagram showing the configuration of a defect inspectingapparatus provided by the present invention which is capable of forminga judgment as to whether or not a defect exists at high S/N ratios forforeign particles ranging from an infinitesimal defect to a defectexhibiting a spreading characteristic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some preferred embodiments of the present invention are explained byreferring to diagrams as follows.

First of all, an inspection object 1 including a defect such as aforeign particle to be inspected is explained by referring to FIGS. 1and 2.

A typical inspection object 1 including a defect such as a foreignparticle to be detected is a semiconductor wafer 1 a on which chips 1 aaeach to be produced as a memory LSI are laid out 2-dimensionally atpredetermined intervals as shown in FIG. 1. Each of the memory chips 1aa each to be produced as a memory LSI includes memory-cell areas 1 abwhich occupy a largest region, peripheral-circuit areas 1 ac eachincluding a decoder and a control circuit and other areas 1 ad. In eachof the memory-cell area 1 ab, a repetitive pattern of memory cells witha minimum line width of typically about 0.1 to 0.3 μm are laid outregularly in 2 dimensions. In a peripheral-circuit area 1 ac, on theother hand, a non-repetitive pattern of memory cells with a minimum linewidth of typically about 0.2 to 0.4 μm are laid out irregularly in 2dimensions. An example of the other areas 1 ad is a bonding area with aminimum line width of typically about 10 μm including substantially nopattern.

Another typical inspection object 1 including a defect such as a foreignparticle to be detected is a semiconductor wafer 1 b on which chips 1 baeach to be produced typically as a microcomputer LSI are laid out2-dimensionally at predetermined intervals as shown in FIG. 2. Each ofthe chips 1 ba each to be produced typically as a microcomputer LSIincludes main areas such as a register-set area 1 bb, a memory-unit area1 bc, a CPU-core area 1 bd and an input/output-unit area 1 be. It shouldbe noted that FIG. 2 conceptually shows the memory-unit area 1 bc andthe register-set area 1 bb each as a matrix to indicate a repetitivematrix but shows the CPU-core area 1 bd and the input/output-unit area 1be each as a hatched area to represent a non-repetitive pattern. In theregister-set area 1 bb and the memory-unit area 1 bc, a repetitivepattern of elements with a minimum line width of typically about 0.1 to0.3 μm are laid out regularly in 2 dimensions. In the CPU-core area 1 bdand the input/output-unit area 1 be, on the other hand, a non-repetitivepattern of elements with a minimum line width of typically about 0.1 to0.3 μm are laid out irregularly in 2 dimensions.

As described above, on a semiconductor wafer used as an inspectionobject 1 including a defect such as a foreign particle to be detected,chips are laid out regularly. However, a chip has a minimum line widthwhich varies from area to area. In addition, elements in a chip may forma repetitive pattern, a non-repetitive pattern or no pattern. Thus, theinspection object 1 can have a variety of possible forms.

With the defect inspecting apparatus and the defect inspection methodprovided by the present invention to detect a defect such as a foreignparticle, a 0th-order diffraction light coming from a line-shapedpattern comprising a group of straight lines in a non-repetitive-patternarea in a chip on such an inspection object 1 is prevented from hittingincidence eyes 20 a and 20 c of an objective lens as shown in FIGS. 12and 21. At the same time, scattered lights coming from a defect such asa foreign particle existing in the non-repetitive-pattern area arereceived as a detection signal from the defect such as a foreignparticle so that the coordinates of the position of the defect can bedetermined.

In addition, while there may be variations in background signal causedby subtle differences among processes, which do not indicate a defect,and noise observed in the detection, with the defect inspectingapparatus and the defect inspection method provided by the presentinvention to detect a defect such as a foreign particle, it is possibleto improve the sensitivity to detect a defect such as a foreign particleand the throughput by setting a threshold value used as a criterion inthe extraction of such a defect.

The following description explains a first embodiment implementing adefect inspecting apparatus provided by the present invention to detecta defect such as a foreign particle by referring to FIGS. 3 and 4.

As shown in FIG. 3, the first embodiment implementing a defectinspecting apparatus for detecting a defect such as a foreign particlecomprises: a stage unit 300 comprising a substrate mounting base 304, x,y and z stages 301, 302 and 303 and a stage controller 305; 3illumination optical systems 100 having a laser-beam source 101, a beamsplitter comprising a concave lens 102 and a convex lens 103 and anillumination lens 104 having a conical surface; a detection opticalsystem 200 including a detection lens 201, a spatial filter 202, animage formation lens 203, an ND (Neutral Density) filter 207, a beamsplitter 204, a polarization device 208 and one-dimensional detectors(image sensors) 205 and 206 which are each implemented typically by aTDI image sensor; an image-signal processing unit 400 shown in detail inFIG. 4; and a white-color optical system 500 comprising a white-colorlight source 106 and an illumination lens 107.

In particular, it is desirable to employ a TDI image sensor of ananti-blooming type. By employing a TDI image sensor of an anti-bloomingtype, inspection of a substrate for a defect such as a foreign particlein an area in close proximity to a saturation zone becomes possible.

As shown in FIG. 4, the image-signal processing unit 400 includes: anA/D converter 401; a data memory 402 for delaying a signal by a time toinspect 1 chip of typically a substrate on which chips are always laidout as a repetitive pattern; a difference processing circuit 403 findinga difference between signals coming from chips; a difference memory 404for temporarily storing differences in signal between chips; amaximum/minimum removing circuit 405 for removing signals representingan abnormal maximum and an abnormal minimum of the differences insignal; a square computing circuit 406 for computing the square of asignal level s; a signal-level computing circuit 407 for computing thesignal level s; a sample counting circuit 408 for counting the number ofsamples; a square integrating circuit 409 for integrating the square ofthe signal level s; a signal-level integrating circuit 410 forintegrating the signal level s; a sample-count computing circuit 411 forcomputing a sample count n for finding a variation; an upper-criterioncomputing circuit (a positive-threshold-value computing circuit) 412; alower-criterion computing circuit (a negative-threshold-value computingcircuit) 413; a comparison circuit 414 for the upper-criterion computingcircuit 412; a comparison circuit 415 for the lower-criterion computingcircuit 413; and a detection-result output means 417 for storing andoutputting a result of detection of a defect such as a foreign particle.

The image-signal processing unit 400 will be described in detail later.

The 3 illumination optical systems 100 have such a configuration that alight emitted by the laser-beam source 101 passes through the beamsplitter comprising the concave lens 102 and the convex lens 103 andthen the illumination lens 104 having a conical surface, being convertedinto slit-shaped beams 3 which are radiated to a wafer 1 or an inspectedsubstrate 1 mounted on the substrate mounting base 304 from 3 directions10, 11 and 12 on a plane as shown in FIG. 5 with the longitudinaldirections of the slit-shaped beams 3 oriented to the layout directionsof the chips. It should be noted that the reason why the light emittedby the laser-beam source 101 is converted into the slit-shaped beams 3is to realize inspection of a substrate for a defect such as a foreignparticle at a high speed. That is to say, the slit-shaped beams 3radiated in the x-axis scanning direction of the x-axis stage 301 andthe y-axis scanning direction of the y-axis stage 302 to the surface ofthe wafer 1 on which chips 2 are laid out each have a shape resembling aslit which is narrow in the y-axis scanning direction of the y-axisstage 302 but wide in the vertical direction, that is, the x-axisscanning direction of the x-axis stage 301 as shown in FIG. 5. In thisway, the slit-shaped beams 3 are radiated to form an image of thelaser-beam source 101 in the direction of the y axis but radiated asparallel beams in the direction of the x axis. It should be noted thatthe slit-shaped beams 3 can be radiated from the 3 directions 10, 11 and12 individually or radiated in such a way that those from the 2directions 10 and 12 are radiated at the same time.

By the way, the reason why the longitudinal directions of theslit-shaped beams 3 radiated to the wafer (inspected substrate) 1 areoriented in the layout direction of the chips on the wafer 1perpendicularly to the y-axis scanning direction of the y-axis stage 302is to sustain an integration direction of the TDI image sensors 205 and206 in an orientation parallel to the scanning direction of the stage.In this way, as shown in FIG. 14, an ordinary TDI image sensor can beemployed and, in addition, image signals coming from different chips canbe compared with each other in a simple way. At the same time,coordinates of the position of a detected defect can be found with ease.As a result, is possible to realize inspection of a substrate for adefect such as a foreign particle at a high speed. In particular, theillumination lens 104 having a conical surface is required in order toorient the slit-shaped beams 3 radiated to the wafer (inspectedsubstrate) 1 from the directions 10 and 12 in the layout direction ofchips on the wafer 1 perpendicularly to the y-axis scanning direction ofthe y-axis stage 302.

FIG. 6 is a diagram showing the illumination lens 104 having a conicalsurface. The illumination lens 104 has a cylindrical shape with focaldistances varying at locations along the longitudinal direction of thecylindrical shape. That is to say, the illumination lens 104 is a lenswith a linearly varying focal distance. Even if beams are radiated in aslanting direction at gradients Φ1 and α1 as shown in FIG. 6, it ispossible to convert the beams into a slit-shaped beam 3 which isconverged in the direction of the y axis and collimated in the directionof the x axis. That is to say, by using the illumination lens 104, it ispossible to radiate parallel beams in the direction of the x axis asshown in FIG. 9( a) at a gradient Φ1 of approximately 45 degrees. Byradiating the parallel slit-shaped beams 3 in the direction of the xaxis as shown in FIG. 9( a), a diffraction-light pattern can be obtainedfrom a circuit pattern with its group of main straight lines oriented inthe directions of the x and y axes, allowing the beams 3 to be shield edby the spatial filter 202.

Next, a method to manufacture the illumination lens 104 having a conicalsurface is explained by referring to FIGS. 7 and 8. Made of a materialsuch as glass or quartz, a cone 23 having a predetermined bottom areaand a predetermined height is created in a polishing process. Then, alens is cut out from the cone 23 at a predetermined cross section tomake the lens 104 having a conical surface. A curved surface of a lensnaturally required in the present invention like the one shown in FIG. 6is actually not a conical surface but must be a curved surface 24 likeone shown in FIG. 8. Since the cubic body shown in FIG. 8 is not a not abody symmetrical with respect to an axis of rotation, however, it isdifficult to polish such a body. For this reason, the lens 104 isapproximated by the cone 23 shown in FIG. 7. There will be no problem inpractical use provided that the lens has an N. A. in the range 0.02 to0.2.

For the shape of the surface of the cone 23 shown in FIG. 7, Eq. (1)given below holds true:

x ² +y ²=(z×tan θ1)²   (1)

where the symbol θ1 is the vertical angle with the vertex of the cone 23positioned at the origin.

As for the curved surface 24 shown in FIG. 8, Eq. (2) given below holdstrue:

(x−z×tan θ2)² +y ²=(z×tan θ2)²   (2)

where the symbol θ2 is likewise the vertical angle with the vertex ofthe cone 23 positioned at the origin.

It should be noted that the method of making the conical lens 104 is notlimited to what is described above. For example, it is also possible toadopt another technique such as an injection molding technique whereby amaterial such as plastic is flowed into a mold with a conical surfacemade in advance. As another method, there is also known a techniquewhereby a glass substrate is mounted on a conical surface made inadvance and the substrate is then melted.

The conical lens 104 provided by the present invention implementsillumination which is critical in the direction of the y axis andcollimated in the direction of the x axis. Configurations for suchimplementation are shown in FIGS. 9( a) and 9(b). A light emitted by thelaser-beam source 101 is radiated to the conical lens 104 by way of abeam expander comprising the concave lens 102 and the convex lens 103.In the conical lens 104, the light is radiated in a collimated form dueto the fact that there is no lens effect in the direction of the x axis.In addition, since the curvature at one edge of the conical lens 104 isdifferent from the curvature at the other edge, the conical lens 104 hasdifferent focal distances. At the same time, the light is focused on thesurface of the wafer 1 by the curvatures of the conical lenses in thedirection of the y axis.

FIG. 10 shows a top view of the 3 illumination optical systems 100 whichemploy a single laser-beam source 101. A laser beam emitted by thelaser-beam source 101 is split by an optical splitting element 110implemented typically by a half mirror into 2 paths. A laser beam alongone of the optical paths is reflected by mirrors 111 and 112 beforebeing directed by a mirror 113 downward toward the concave lens 102. Asa result, an illumination beam from a direction 11 is obtained. A laserbeam along the other optical path travels to an optical splittingelement 114 also implemented typically by a half mirror. At the opticalsplitting element 114, the laser beam is further split into to twopaths. A laser beam along one of the optical paths is reflected by amirror 115 before being directed by a mirror 117 downward toward theconcave lens 102. As a result, an illumination beam from a direction 10is obtained. A laser beam along the other optical path is directed by amirror 116 downward toward the concave lens 102. As a result, anillumination beam from a direction 10 is obtained.

When it is desired to radiate a laser beam to the concave lens 102 onlyfrom the direction 11, by the way, the optical splitting element 110 canbe replaced by a mirror element 118. When it is desire to radiate laserbeams to the concave lens 102 only from the directions 10 and 12, on theother hand, the optical splitting element 110 is just removed from theoptical paths or replaced with a proper optical device. Likewise, whenit is desired to radiate a laser beam to the concave lens 102 only fromthe direction 12 without the laser beam from the direction 10, theoptical splitting element 114 can be replaced by a mirror element 119.

It should be noted that, as the laser-beam source 101, it is possible toemploy a high-output YAG laser SHG for generating a second harmonic wavewith a wavelength of 532 nm for a splitting reason even though thewavelength does not have to be 532 nm. In addition, the laser-beamsource does not have to be a YAG laser SHG. That is to say, as thelaser-beam source 101, it possible to use a source of another kind suchas an Ar laser, a nitrogen laser, an He—Cd laser or an exima laser.

In the detection optical system 200, a light emitted by the wafer 1passes through the detection lens (objective lens) 201, the spatialfilter 202, the image formation lens 203, the ND filter 207, thepolarization device 208 and the beam splitter 204 before being inspectedby the detectors 205 and 206 which are each implemented typically by aTDI image sensor. The spatial filter 202 shield s aFourier-transformation image formed by a diffraction light reflected bya repetitive pattern. The ND filter 207 adjusts the quantity of lightwithout regard to wavelength bands. The spatial filter 202 is placed ina spatial-frequency area of the objective lens 201 at which aFourier-transformation image formed by a diffraction light reflected bya repetitive pattern is to be shielded. That is to say, the spatialfilter 202 is placed at an image formation position of the Fouriertransformation which corresponds to an emission eye. The polarizationdevice 208 shield s polarization components of reflected scatteredlights which are generated by an edge of a circuit pattern when theillumination optical system 100 radiates a polarization light. However,the polarization device 208 passes some polarization components ofreflected scattered lights which are generated by a defect such as aforeign particle. Thus, the polarization device 208 is not necessarilyrequired by the present invention. In the detection optical system 200,an image of an illuminated area 4 on the wafer 1 shown in FIG. 5 isformed on the detectors 205 and 206 by the image formation lens 203 andthe objective lens 201 serving as a relay lens. That is to say,reference numeral 4 also denotes a photo-sensitive area on the detectors205 and 206 which are each implemented by typically a TDI image sensoras described above.

When slit-shaped beams 3 are radiated to the wafer (substrate) 1 havinga variety of circuit patterns formed thereon, reflected diffractionlights or scattered lights are emitted from the surface of the wafer 1,the circuit patterns and defects such as foreign particles. Each of theemitted lights travels to the detectors 205 and 206 by way of thedetection lens 201, the spatial filter 202, the image formation lens203, the ND filter 207, the polarization device 208 and the beamsplitter 204. In the detectors 205 and 206, the light is converted intoan electrical signal.

It should be noted that the shown order in which the ND filter 207, thepolarization device 208 and the beam splitter 204 are placed along theoptical path is typical. In particular, if the ND filter 207 is placedbehind the beam splitter 204, the intensities of light beams arriving atthe detectors 205 and 206 can be controlled independently of each other.

In addition, the transmittance and reflectance rates of the beamsplitter 204 do not have to be 50%. For example, the transmittance rateand the reflectance rate can be set at 1% and 99% respectively. Bysetting the transmittance and reflectance of the beam splitter 204 atsuch values that the intensity of the beam hitting one of the detectors205 and 206 is about 1/100 of the intensity of the beam hitting one ofthe other detector in this way, signals will be generated by the 2detectors 205 and 206 which receive beams having different intensities.Thus, the dynamic range of the detectors 205 and 206 appears improved.As a result, the image-signal processing unit 400 is capable ofobtaining a detection signal of a defect such as a foreign particle withan improved dynamic range from signals generated by the detectors 205and 206. In particular, a signal generated by one of the detectors 205and 206 as a result of a photo-electrical conversion of a light with alarge intensity has its a large-intensity component indicating a defectemphasized. On the other hand, a signal generated by the other detectoras a result of a photo-electrical conversion of a light with a smallintensity has its a small-intensity component close to the backgroundalso emphasized. Accordingly, by identifying a correlation between the 2emphasized signals such as the ratio of the signal to the other, thedynamic range of a signal representing a defect can be enhanced.

By adjusting the illumination (power) of a beam radiated by thelaser-beam source 101 employed in the illumination optical systems 100,the dynamic range can also be changed. Thus, the beam splitter 204 andone of the detectors 206 can be eliminated.

The following description explains a relation between the slit-shapedbeam 3 radiated by the illumination optical system 100 provided by thepresent invention to the wafer 1 and the detection optical system 200also provided by the present invention in concrete terms. FIG. 5 is adiagram showing a top view of directions of illumination by theslit-shaped beam 3 and a direction of detection by the one-dimensionaldetectors 205 and 206 which are each implemented typically by a TDIimage sensor as described earlier. In the example shown in the figure,the slit-shaped beam 3 illuminates the wafer 1 on which a pattern 2 isformed. Reference numeral 4 denotes an image formed by theone-dimensional detectors 205 and 206 employed in the detection opticalsystem 200. Slit-shaped beams 3 are radiated to the wafer 1 fromdirections 10, 11 and 12 on a plane.

FIG. 11( a) is an explanatory diagram for supplementing FIG. 5. In FIG.11( a), reference numeral 10 denotes an illumination direction andreference numeral 14 denotes a detection direction perpendicular to thesurface of a wafer 1 on which the axes x and y are laid. A sphericalsurface 17 is an imaginary surface assumed in thinking of an apertureposition of the objective lens 201 employed in the detection opticalsystem 100 shown in FIG. 5. An illumination light traveling in thedirection 10 and a detection light traveling in the direction 14intersect the spherical surface 17 at cross points 15 and 16respectively.

On the other hand, FIG. 11( b) is a diagram showing the state ofemission of a diffraction light which is obtained as a result of anillumination in the direction 10. A light resulting from true reflectionof the illumination light in the direction 10 travels in an emissiondirection 19, intersecting the spherical surface 17 at a cross point 18.This light traveling in the emission direction 19 is referred to as a0-order light. Imagine a cone oriented upside down perpendicularly tothe plane of the x and y axes with the vertex thereof coinciding with apoint of illumination on the plane as shown in FIG. 7( b). The beam 3traveling in the illumination direction 10 and the reflected 0th-orderlight traveling in the emission direction 19 form the sides of alongitudinal cross section of the cone. That is to say, a locus of theintersection point of the reflected 0th-order light traveling in theemission direction 19 and the imaginary spherical surface 17 form thecircumference of the bottom of the cone.

Thus, when seen from the direction of the normal line, the locus is astraight line parallel to the x and y axes.

By the way, reference numeral 20 a shown in FIGS. 12 and 13 denotes theaperture of the objective lens 201 employed in the detection opticalsystem 200 which is not inclined or has a gradient β1 of 0.

In this case, assume that angles Φ1 and Φ2 formed by the illuminationdirections 10 and 12 with the y axis respectively are both set at atypical value of about 45 degrees. With the optical axis of thedetection optical system 200 oriented perpendicularly to the surface ofthe wafer 1, that is, with the gradient β1 set at 0, as shown in FIG. 3,the numerical aperture (N.A.) of the detection lens (objective lens) 201and the angle α1 of the illumination light shown in FIG. 3 should be setin a range defined by relations (3) shown below with a condition thatthe 0th-order diffraction lights 21 x and 21 y generated by a circuitpattern with its group of main lines thereof oriented in the directionsof the x and y axes respectively are guided not to enter the eye of thedetection lens 201 as shown in FIG. 12. That is to say, by setting theangles Φ1 and Φ2 formed by the illumination directions 10 and 12 withthe y axis respectively both at a typical value of about 45 degrees andby setting the numerical aperture (N.A.) of the detection lens(objective lens) 201 and the angle α1 of the illumination light shown inFIG. 3 in a range satisfying relations (3) shown below, the 0th-orderdiffraction lights 21 x and 21 y generated by a circuit pattern with itsgroup of main lines thereof oriented in the directions of the x and yaxes respectively can be prevented from entering the aperture 20 a ofthe detection lens 201 even if the circuit pattern is a non-repetitivepattern.

N.A.<cos α1×sin Φ1 and

N.A.<cos α1×sin(π/2−Φ1)   (3)

It should be noted that, for al equal to or smaller than 30 degrees, thenumerical aperture (N.A.) of the objective lens 201 can be set at avalue equal to about 0.4 or smaller.

These conditions are specially effective for products such as aperipheral-circuit area 1 ac having a non-repetitive pattern on a memoryLSI 1 aa, an input/output-unit area 1 be and a CPU-core area 1 bd havinga non-repetitive pattern on an LSI 1 ba such as a microcomputer and alogic LSI having a non repetitive pattern.

In many cases, LSI patterns are each created in a perpendicular-parallelposture, that is, to contain a group of parallel and perpendicular mainstraight lines. Thus, 0th-order lights are emitted by these patterns ina specific direction. For this reason, by preventing the 0th-orderlights emitted by these patterns from hitting the objective lens 201,diffraction lights emitted by most of these patterns can be eliminated,making it possible to detect only a diffraction light reflected by adefect such as a foreign particle with ease. To put it concretely, thereare an increased number of areas which contain a defect such as aforeign particle detectable with a high degree of sensitivity due to thefact that the level of a detection signal generated by the circuitpattern is lowered.

As a mater of course, in the case of a non-repetitive pattern,higher-order (such as the first order, the second order and so on)diffraction lights enter the aperture 20 a of the objective lens 201.Thus, higher-order diffraction lights appear as a group of straightlines parallel to the 0th-order diffraction lights 21 x and 21 y shownin FIG. 12. However, the higher-order diffraction lights can also beeliminated by shielding the lights by using the spatial filter 202 whichhas a fine band shape.

In addition, it is necessary to inspect the substrate (wafer) 1 forthings such as a foreign particle or a defect caught in a dent betweenprotrusions like wires or an etching remnant. As described above,however, it is also necessary to radiate slit-shaped beams 3 havingtheir longitudinal directions oriented in the direction of the x axis tothe substrate 1 being inspected from the directions 10 and 12 eachforming an angle of about 45 degrees with the y axis in order to preventa 0th-order diffraction light generated by a non-repetitive patternexisting on the substrate 1 from entering the objective lens 201. Inthis case, things such as protruding wires serve as a disturbance,making it difficult to provide sufficient illumination.

For the reason described above, in most cases, LSI patterns are eachcreated in a perpendicular-parallel posture, that is, to contain a groupof parallel and perpendicular main straight lines as described above sothat, by radiating a slit-shaped beam 3 to the substrate 1 from thedirection 11 parallel to the y axis, a dent between things such as wirescan be illuminated sufficiently. In particular, a wiring pattern of amemory LSI is a straight-line pattern with a length of several mm inmany cases so that most inspections can be done by illumination fromthis direction 11. In addition, in the case of a 90-degree direction forsome patterns, an inspection can be done by rotating the wafer by 90degrees or by orienting the illumination direction in the direction ofthe x axis.

When radiating the slit-shaped beam 3 from the direction 11, however,the 0th-degree diffraction light 21 y′ enters the aperture 20 a of theobjective lens 201 but the 0th-degree diffraction light 21 x′ does notas shown in FIG. 13. It is thus necessary to eliminate this 0th-degreediffraction light 21 y′ by shielding the light 21 y′ using the spatialfilter 202. At that time, as a matter of course, the higher-orderdiffraction lights can also be eliminated by shielding the light 21 y′using the spatial filter 202.

The above description explains how to eliminate particularly a 0th-orderdiffraction light reflected by a non-repetitive pattern in the case of anon-repetitive pattern existing in a chip 2 on the substrate 1 beinginspected. However, the chip 2 may be a memory LSI 1 aa including amemory-cell area 1 ab or an LSI 1 ba such a microcomputer including aregister-set area 1 bb and a memory-unit area 1 bc. Since thememory-cell area 1 ab, the register-set area 1 bb and the memory-unitarea 1 bc are repetitive patterns, it is necessary to shield diffractionlights (or diffracted interference light beams) generated by theserepetitive patterns by using the spatial filter 202. In a word, arepetitive pattern, a non-repetitive pattern and a non pattern coexistwith each other in the chip 2 and, further, the line width varies frompattern to pattern. For this reason, a shielding pattern of the spatialfilter 202 is normally set to eliminate a diffraction light generatedtypically by a repetitive pattern having a high degree ofrepetitiveness. In addition, in the case of a detection optical system200 employing a spatial filter 202 with a variable shielding patternsuch as ones disclosed in Japanese Patent Laid-open No. Hei 5-218163(U.S. Pat. No. 5,463,459) and Japanese Patent Laid-open No. Hei6-258239, the shielding pattern is changed in accordance with a circuitpattern of the chip 2. As an alternative, a plurality of spatial filters202 with different shielding patterns are provided in advance and one ofthem appropriate for the circuit pattern in the chip 2 is selected.

The following description explains how to adjust the detectionsensitivity in accordance with the size of a defect such as a foreignparticle to be detected. That is to say, the detection sensitivity isexpected to increase even at the expense of a lower throughput byreducing the size of the detection pixel on the inspection object 1 ofthe one-dimensional detectors (image sensors) 205 and 206 which are eachimplemented by typically a TDI image sensor as described above. Thus,when detecting a defect such as a foreign particle with a dimension notexceeding 0.1 μm, the defect inspecting apparatus is switched to adetection optical system 200 which decreases the pixel size. To put itconcretely, it is desirable to provide 3 detection optical systems ofdifferent types typically appropriate for respectively images with sizesof 2 μm, 1 μm and 0.5 μm on the wafer 1 for pixels such as those of theTDI image sensors. As a technique of implementation of the detectionoptical system 200, the entire optical system 200 can be replaced byanother one, or only the lens (group of lenses) 203 or the lens (groupof lenses) 201 is replaced. In this case, the configurations of thelenses may be designed so that the switching can be done withoutchanging the lengths of the optical paths between the wafer 1 and theone-dimensional detectors 205 and 206 which are each implemented bytypically a TDI image sensor as described above. If the design isdifficult, it is also possible to use a mechanism which tolerateschanges in distances to the sensors accompanying switching of thedetection optical system 200 from one lens to another. As anotheralternative, the detection optical system 200 can also be switched fromone lens to another with a different pixel size of the sensor itself.

The following description explains a concrete embodiment of a relationbetween the slit-shaped beams 3 radiated from the 3 directions and theTDI image sensors 205 and 206 by referring to FIG. 14. FIG. 14 is adiagram showing a relation between a TDI image 4 on the wafer 1 andslit-shaped beams 3-10 and 3-12 radiated from the directions 10 and 12respectively. When beams obtained as a result of splitting a laser beamgenerated by a single laser-beam source 101 are radiated from thedirections 10 and 12 as shown in FIG. 10, the beams interfere eachother, resulting in variations in intensity in the illumination zone. Inorder to solve this problem, the beams 3-10 and 3-12 are radiated insuch a way that they do not interfere each other in the zone of the TDIimage 4 as shown in FIG. 14 in order to eliminate effects of theinterference. When the TDI image sensors 205 and 206 are used, theproblem caused by such a positional shift does not arise since detectionoutputs in the zone of the image 4 are integrated in the direction ofthe y axis in the zone in synchronization with the movement of they-axis stage. Also when the slit-shaped beam 3-11 radiated from thedirection 11 is used, the beams 3-10, 3-11 and 3-12 are similarlyradiated so that they do not interfere each other in the zone, causing aproblem of an overlap of the 3 beams. It is needless to say that theproblem of interference can be avoided in the same way for any 2 of the3 slit-shaped beams 3-10, 3-11 and 3-12 radiated from the directions 10,11 and 12 respectively.

As shown explicitly in none of the figures, when the slit-shaped beams3-10 and 3-12 are radiated from the directions 10 and 12 respectively tothe same location, they will interfere each other. Since the interferingbeams are inclined in the direction of the y axis, however, variationsin illumination intensity caused by the interference are reduced by aneffect of an integration carried out by the TDI image sensors 205 and206. It is thus not necessary to radiate the slit-shaped beams 10 and 12so that they do not interfere each other as shown in FIG. 14.

The following description explains a second embodiment implementing adefect inspecting apparatus provided by the present invention fordetecting a defect such as a foreign particle by referring to FIG. 15.As shown in the figure, in order to increase the intensity of ascattered light coming from a defect such as a foreign particle, theoptical axis of the detection optical system 200 is inclined by an angleβ1 from the vertical direction. The rest of the configuration is thesame as the first embodiment shown in FIG. 3.

The reason why the optical axis of the detection optical system 200 isinclined by an angle β1 from the vertical direction is to increase theintensity of a scattered light coming from a defect such as a foreignparticle as shown in FIG. 16 and, hence, to increase the detectionsensitivity. The increase in light intensity is attributed to thefollowing cause. A particle or a foreign particle larger in size than afraction of the illumination wavelength generates a light 51 with a highintensity scattered in the forward direction. On the other hand, a light52 generated by an area such as a dry spot with a size close to 1/10 ofthe wavelength or smaller is scattered almost in the forward directionso that the intensity of the scattered light from the infinitesimalparticle in the forward direction is relatively high. As a result, ifthere are a plurality of dry spots on the surface of a circuit patternamong detection pixels, the total intensity is represented by a curve 53shown in FIG. 16. Thus, by taking the scattered lights traveling in theforward direction, an infinitesimal particle or a defect can be detectedfrom a surface dry spot.

If TDI (Time Delay Integration) sensors are used as the detectors 205and 206, however, the optical axis of the detection optical system 200can not be inclined due to a focal depth. Thus, in the case of thesecond embodiment, one-dimensional sensors are employed. As analternative, the magnification of a set comprising the detection lens201, the spatial filter 202 and the image formation lens 203 employed inthe detection optical system 200 is doubled or increased by severaltimes and, as shown in FIG. 17, the TDI image sensors 205 and 206 areinclined at a gradient β2 expressed by Eq. (4) below. In this way, themagnification can be adjusted for the entire surface.

tan β2=M×tan β1   (4)

where the symbol M denotes the magnification of the set comprising thedetection lens 201, the spatial filter 202 and the image formation lens203.

It should be noted that, if one-dimensional sensors are employed, theinclination at the gradient β2 is not required.

The next description explains detection of scattered lights generated bya defect such as a foreign particle using the one-dimensional detectors205 and 206 each implemented typically by a TDI image sensor byelimination of diffraction lights generated by a non-repetitive patternand a repetitive pattern in the second embodiment. Also in the case ofthe second embodiment, slit-shaped beams 3 are radiated to the substrate(or wafer) 1 being inspected in the same way as that shown in FIG. 5.When a slit-shaped beam 3 is radiated from the direction 10 as shown inFIG. 11( a), the state of emission of a diffraction light generated bythe substrate 1 is shown in FIG. 11( b) as is the case with the firstembodiment. That is to say, a light resulting from true reflection ofthe illumination light in the direction 10 travels in the emissiondirection 19, intersecting the virtual spherical surface 17 at the crosspoint 18, and the light traveling in the emission direction 19 isreferred to as a 0th-order light. The beam 3 traveling in theillumination direction 10 and the reflected 0th-order light traveling inthe emission direction 19 form the sides of a longitudinal cross sectionof an imaginary cone oriented upside down perpendicularly to the planeof the x and y axes with the vertex of the cone coinciding with a pointof illumination on the plane. Thus, a locus of the intersection point ofthe reflected 0th-order light traveling in the emission direction 19 andthe imaginary spherical surface 17 form the circumference of the bottomof the cone as shown in FIG. 18. Accordingly, in the case of arepetitive pattern, when seen from the direction of the normal line, thelocus of the 0th-order light is a straight line parallel to the x and yaxes.

In particular, in the case of a repetitive pattern, the local maximum ofthe 0th-order diffraction light is located at an intersection point 22of the group of straight lines. Thus, the aperture 20 b of the objectivelens 201 employed in the detection optical system 200 inclined at agradient β1 is like one shown in FIG. 18. When the aperture 20 b is seenfrom a direction 14, that is, the direction of the optical axis, the0th-order diffraction light 22 appears to be emitted to an intersectionpoint of a curve and a straight line shown in FIG. 19( a).

Then, by shielding these diffraction lights by means of a shieldingportion 207 having a straight-line shape like one shown in FIG. 19( b)in the spatial filter 202, a signal generated by a pattern can beremoved. In addition, if the shape and the pitch of a repetitive patternon the wafer 1 change, the pitch of the locus of the directions of the xand y axes changes, centering at an emission point 18 shown in FIG. 18.Thus, in the aperture 20 b, the pitch and the phase of the diffractionlight 22 change. In order to shield these diffraction lights, it isnecessary to change the pitch and the phase of the straight-line-shapedshielding portion 207.

As described above, a diffraction light generated by a repetitivepattern can be shielded by the spatial filter 202. The next descriptionexplains elimination of diffraction lights generated by a non-repetitivepattern. In general, a non-repetitive pattern is a straight-line patternoriented in the directions of the x and y axes. Thus, when a slit-shapedbeam 3 is radiated from the direction 10, 0th-order diffraction lights21 x and 21 y in the directions of the x and y axes respectively shownin FIG. 20 are generated as is the case shown in FIG. 12. Since theoptical axis 200 of the detection optical system 200 is inclined at thegradient β1, however, the intensity of a light scattered by aninfinitesimal particle is high but the 0th-order diffraction light 21 xemitted in the direction of the y axis enters the aperture 20 b of theobjective lens 201. Thus, also in the case of a non repetitive pattern,it becomes necessary to shield the 0th-order diffraction light 21 x byusing the spatial filter 202.

Since a diffraction light beam generated by a repetitive pattern isdifferent from a 0th-order diffraction light pattern for anon-repetitive pattern as described above, it is necessary to provideboth the diffraction-light patterns to the spatial filter 202. If anattempt is made to shield both the diffraction-light patterns by usingthe spatial filter 202, however, the intensity of a scattered lightpassing through the spatial filter 202 is attenuated, causing thesensitivity to deteriorate.

In order to solve the problem described above, the optical axis of thedetection optical system 200 is erected to position the aperture of theobjective lens 201 at a location 20 a and to radiate slit-shaped beams 3to a non-repetitive pattern from the directions 10 and 12 as is the casewith the first embodiment. In this way, 0th-order light patterns 21 xand 21 y can be prevented from entering the aperture 20 a of theobjective lens 201, making it possible to detect a defect such as aforeign particle existing on a non-repetitive pattern.

As is obvious from the description of the first embodiment givenearlier, however, it is necessary to radiate a slit-shaped beam 3 fromthe direction of the y axis 11 as shown in FIG. 13 in an attempt todetect a defect such as a foreign particle existing in a dent betweenwires. In this case, however, a 0th-order diffraction light 21 y′ entersthe aperture 20 a of the objective lens 201 as shown in FIG. 13, makingit necessary to shield the light 21 y′ by means of the spatial filter202. Nevertheless, the detection of a defect such as a foreign particleexisting in a dent between wires is not the principal part of thedetection of defect in general including foreign particles. Since apattern being inspected is identified, a measure can be taken during theimage processing.

If the conditions described above are configured in a way describedbelow, the conditions can be satisfied. To put it in detail, theilluminations from the directions 10 and 12 each forming an angle of 45degrees with the y axis are given up and only a slit-shaped beam 3 isradiated from the direction of the y axis 11. The optical axis of thedetection optical system 200 is inclined from the vertical directiontoward the directions of the x and y axes to place the aperture of theobjective lens 201 at a position denoted by reference numeral 20 c inFIG. 21. In this way, 0th-order light patterns 21 x′ and 21 y′ can beprevented from entering the aperture 20 c of the objective lens 201. Inthis configuration, the spatial filter 202 can be designed to shieldonly a diffraction light beam generated by a repetitive pattern. Inaddition, it is possible to prevent deterioration of the intensity of ascattered light passing through the spatial filter 202 from a defectsuch as a foreign particle.

In this case, however, it is necessary to decrease the N.A. of theobjective lens 201.

The problem is the focuses of the detectors 205 and 206. As shown inFIG. 17, the configuration with the inclined detectors 205 and 206allows the focuses to be adjusted in the entire image formation area. Inthis case, it will be insufficient to merely incline the detectors 205and 206 at a gradient β2. Instead, it is necessary to incline them atthe gradient β2 and in a direction perpendicular to the direction 14. Inaddition, since the detection optical system 200 employs a telecentricoptical system, the horizontal magnification by no means changes at aportion where the focal positions are different from each other.

Next, the following description explains a third embodiment implementinga defect inspection apparatus provided by the present invention fordetecting a defect such as a foreign particle. The third embodiment isinferior to the first and second embodiments.

In the case of the third embodiment, a cylindrical lens 104′ is employedin place of the conical lens 104 as shown in FIG. 22. By using thecylindrical lens 104′, slit-shaped beams 3′ with the longitudinaldirections thereof oriented to the illumination directions 10 and 12 areradiated to the surface of the wafer 1. The illumination directions 10and 12 are inclined from the layout direction of chips created on thewafer 1 by an angle of about 45 degrees. The slit shapes of the beamsare parallel to the incidence plane of the illumination. As a matter ofcourse, since the slit-shaped beams 3′ are beams parallel to each otherin their longitudinal direction, they do not intercept each other in thetransversal direction. It should be noted that diffraction lightsgenerated by repetitive and non-repetitive patterns created on chips 2on the wafer 1 are handled in the same way as the first and secondembodiments.

In the case of the third embodiment, it is necessary to set the y-axisscanning direction of the stage in an orientation perpendicular orparallel to the chips in order to make chip comparison simple. Inaddition, since the integration direction of the TDI image sensors isnot parallel to the y-axis scanning direction of the stage in the thirdembodiment, TDI image sensors can not be used as the detectors 205 and206. It is thus necessary to employ one-dimensional linear sensors asthe detectors 205 and 206. In the case of a linear sensor, since anoptical signal from an area narrower than the width of the illuminationbeam is detected, it is desired to squeeze the illumination beam 3′ to awidth close to the image 4 of the sensor in order to utilize theillumination beam 3′ with a high degree of efficiency. To put itconcretely, assume that the pixel size of the sensor is 13 μm and themagnification of the optical system is 6.5 times. In this case, thepixel size of the image of the sensor formed on the wafer 1 is 2 μm. Letthe wavelength of the used laser be 532 nm. In this case, it isdesirable to set the N.A. (numerical aperture) of the lens 104′ employedin a direction perpendicular to the longitudinal direction of the sensorat about 0.5 in Eq. (5) given below. Of course, this value is selectedonly in order to increase the efficiency of the illumination. If it isnot necessary to increase the efficiency of the illumination, a smallerN.A. can be used.

d=1.22×λ/N.A.   (5)

where the symbol d denotes the half band width and the symbol λ denotesthe wavelength of the illumination beam.

When TDI image sensors are used as the detectors 205 and 206 in themethod of illumination shown in FIG. 22, the sensors must be special,having a shape like one shown in FIG. 23. That is to say, the specialTDI image sensors have a pixel configuration with an integrationdirection inclined at a gradient Φ1.

The following description explains detection of a defect such as aforeign particle existing on an insulation film such as an oxide filmwith no pattern used as an object of inspection.

FIG. 24 is a diagram showing a state of scattering of lights by atransparent film such as an oxide film. Assume that a very smallinfinitesimal particle or a foreign particle 34 with a size equal to afraction of the wavelength of the illumination beam exists on thesurface of an oxide film 32 on a substrate 33. In this case, theparticle generates a beam having a spherical polarization plane. That isto say, a beam is radiated to the surface of the oxide film 32 and tothe detectors at the same time. The beam emitted by a particle with sucha polarization plane is a result of reflection of the beam radiated tothe oxide film 32 by a boundary surface between the oxide film 32 and anunderlying layer 33. The reflected beam interferes the beam radiateddirectly to the defector, resulting in strength in the emissiondirection. As a result, outputs of the detection in directions 36, 37and 38 are different from each other. The intensity distribution changesin dependence on the thickness of the oxide film and the refractiveindex. As a result, the intensity of a detection beam detected from thesame direction changes, causing the sensitivity to also vary as well.

According to consideration based on this model, however, the output of adetected light remains unchanged without regard to the direction of theillumination. In addition, experiments have proven that the output of adetected beam does not change even if the angle of incidence of theillumination light is changed.

However, optical interference can be eliminated by radiation of a whitelight. As a matter of fact, the first and second embodiments areprovided with a white-illumination optical system 500 for detecting aforeign particle on the insulation film 32 such as an oxide film. Thus,in order to detect a foreign particle on the insulation film 32, thewhite-color light source 106 is turned on while the laser-beam source101 is turned off. In addition, white-color illumination is also adoptedfor an object of inspection affected by the wavelength of theillumination light.

In the case of white-color illumination, the resulting illumination spotis bigger in size than the visual field of the TDI image sensors.

In addition, when the laser-beam source 101 is used for generating anillumination light, it is necessary to employ an objective lens 201 witha large numerical aperture in order to stabilize the detection output onthe oxide film 32. This is because such an objective lens 201 is capableof detecting most lights emitted from the surface of the wafer 1. If anobjective lens 201 with a small numerical aperture is used, on the otherhand, a plurality of such lenses 201 are required. In this case,detection outputs of the lenses 201 are integrated. As an alternative, aplurality illumination lights with different wavelengths are used andtheir results of detection are integrated.

In this case, absorption or attenuation of a scattered light generatedby a foreign particle on the film can be assumed to be substantiallynon-existent. In the case of a non-existing foreign particle, lights areemitted in one direction so that, the output in this direction variesdue to interference. If a foreign particle exists, on the other hand,the emitted light is spread in a plurality of emission directions sinceinterference occurs in the form of intensity distribution among theemission directions.

FIG. 25 is a diagram showing the configuration of an embodiment fordetection from a plurality of directions. From lights emitted indirections 213, 214 and 215, detection lenses 210, 211 and 212 formimages which are detected by detectors 213, 214 and 215 respectively.Analog electrical signals obtained as results of photo-electricalconversions carried out by the detectors 213, 214 and 215 are convertedinto digital data by A/D converters 451, 452 and 453 respectively. Thedigital data is then integrated by an integration means 454 andconverted into binary data representing a result of detection by using aproper threshold value.

It should be noted that the number of detection systems including thedetection lenses 210, 211 and 212 does not have to be 3. For example, 2detection systems are OK. In addition, the detection systems in thisembodiment are each implemented by the detection optical system 200shown in FIG. 3. In this case, each of the detection optical systems 200is inclined by a gradient β. Examples of the gradient are β1=0 degreesand β1=45 degrees.

FIG. 26 is diagrams showing changes in detection signal with variationsin oxide-film thickness. To be more specific, FIG. 26( a) is a diagramshowing an intensity-variation change 48 of a light with a certainwavelength. On the other hand, FIG. 26( b) is a diagram showingintensity-variation curves 48, 49 and 50 of 3 lights with differentwavelengths. By integrating results of detection for the lights withdifferent wavelengths shown in FIG. 26( b), variations in integrationresult will be smaller than variations in intensity shown in FIG. 26( a)as is obvious from the figures.

In this case, since we know that the intensity of a detected signal isnot dependent on the angle of incidence of the illumination light,lights with different wavelengths can be radiated at different angles ofincidence or from different directions determined by the angle Φ. Thatis to say, by setting the wavelengths of the slit-shaped beams 3radiated from the directions 10, 11 and 12 at values different from eachother, it is possible to detect a signal indicating a foreign particleon an insulation film such as an oxide film by means of a singledetection optical system 200. The reason why it is possible to detect asignal indicating a foreign particle on an insulation film such as anoxide film by means of a single detection optical system 200 by settingthe wavelengths of the slit-shaped beams 3 radiated from the directions10, 11 and 12 at values different from each other is that there is nomutual interference. As a result, it is possible to avoid an increase incost caused by a need to prepare a plurality of detection opticalsystems 200. With at least 2 beams having different wavelengths, thedetection optical system 200 is capable of correcting color aberration(and a focal distance) with ease. As a result, there is no difficulty inthe implementation as long as 2 beams having different wavelengths areused.

The next description explains a fourth embodiment implementing a defectinspecting apparatus provided by the present invention for detecting adefect such as a foreign particle. By the way, with semiconductordevices miniaturized more and more, a further increase in yield is alsorequired. To put it in detail, a circuit pattern created on asemiconductor substrate such as a semiconductor wafer for making suchsemiconductor devices is subjected to super miniaturization with adesign rule of 0.3 to 0.2 μm or even smaller. For this reason, a foreignparticle existing on the semiconductor substrate causes a semiconductordevice created on the substrate to operate abnormally even if theforeign particle is an infinitesimal molecule with a size of about 0.1μm or smaller or a particle with a size close to that at an atomiclevel.

In such a state of the art to fabricate a semiconductor device, thedefect inspecting apparatus provided by the present invention fordetecting a defect such as a foreign particle is required to have acapability of inspecting a defect such as an infinitesimal foreignparticle existing on a semiconductor substrate such as a semiconductorwafer, on which a circuit pattern undergoing a super-miniaturization bya design rule of 0.3 to 0.2 μm or even smaller exists, with a highdegree of sensitivity at a high speed.

FIG. 35 is a diagram showing the fourth embodiment implementing a defectinspecting apparatus provided by the present invention for detecting adefect such as a foreign particle in a simple and plain manner. FIG. 36is a diagram showing an embodiment implementing an illumination opticalsystem employed in the defect inspecting apparatus.

As shown in FIG. 35, the defect inspecting apparatus for detecting adefect such as a foreign particle comprises: stages 301, 302 and 303 formounting an inspection object 1 such as a semiconductor device or asemiconductor wafer on which a super-miniaturized circuit pattern with adefect thereof to be detected has been created; an illumination-lightsource 101 implemented by a laser-beam source such as a semiconductorlaser, an argon laser, a YAG-SHG laser or an exima laser; anillumination optical system comprising the components 102 to 105 forradiating a high-luminance light emitted by the illumination-lightsource (laser source) 101 to an illumination area 3 on the inspectionobject 1 from a slanting direction as a slit-shaped Gaussian beam 107having a illumination distribution close to the Gaussian distribution asshown in FIG. 37; a detection optical system 200 including a detectionlens (objective lens) 201, a spatial filter 202, an image formation lens203, an ND filter 207 and a beam splitter 204 which are used for formingan image from diffraction lights (or scattered lights) reflected by adetection area 4 to pass through the detection optical system 200;detectors 205 and 206 each implemented typically by a TDI image sensoror a CCD image sensor having a photo-sensitive surface corresponding tothe detection area 4; and an image-signal processing unit 400 fordetecting a defect such as a foreign particle from an image signaloutput by the detectors 205 and 206.

It should be noted that the defect inspecting apparatus also has anautomatic focus control system for controlling formation of an image ofthe surface of the inspection object 1 on the photo-sensitive surface ofthe detectors 205 and 206.

The actual configuration of the illumination-light optical source 101and the illumination optical systems comprising the components 102 to105 is shown in FIG. 36. In the figure, reference numeral 102 denotes aconcave or convex lens for enlarging the diameter of a laser beam 1006emitted by the illumination-light source 101. Reference numeral 103denotes a collimate lens for converting a laser beam output by theconcave or convex lens 102 with an expanding diameter into substantiallyparallel beams. Reference numeral 104 denotes an illumination lens witha conical surface for converging the substantially parallel beamsobtained as a result of the conversion in the collimate lens 103 in thedirection of the y axis and for radiating the converged beams to anillumination area 3 on the inspection object 1 as a slit-shaped Gaussianbeam 1007 having an illumination distribution close to the Gaussiandistribution as shown in FIG. 37. The illumination lens 104 serves as anoptical system having a converging function in the direction of the yaxis.

It should be noted that the concave or convex lens 102 and the collimatelens 103 constitute a beam expander for enlarging the diameter of thelaser beam 1006. Thus, the illumination optical system including thecomponents 102 to 104 can be regarded as a system comprising the beamexpander, the conical lens 104 and a mirror. The beam expander typicallycomprises a collimate lens, a concave lens and a receiver lens. Asdescribed above, the conical lens 104 is used for converging thesubstantially parallel beams obtained as a result of the conversion inthe beam expander in the direction of the y axis and for radiating theconverged beams to an illumination area 3 on the inspection object 1 asa slit-shaped Gaussian beam 1007 having an illumination distributionclose to the Gaussian distribution as shown in FIG. 36. The mirrorreflects the slit-shaped Gaussian beam 1007 output by the conical lens104 and radiates the beam 1007 to the inspection object 1 in a slantingdirection.

By the way, by changing the distance b between the concave or convexlens 102 and the collimate lens 103 or the distance between the concavelens and the receiver lens in the configuration described above, thex-direction width of the luminance beam having an illuminationdistribution substantially resembling the Gaussian distribution can bealtered. That is to say, by adjusting the beam expander, the x-directionlength Lx of the illumination area 3 (or the slit-shaped beam 1007)having an illumination distribution substantially resembling theGaussian distribution can be changed. In addition, by varying thedistance between the conical lens 104 and the inspection object 1, they-direction length Ly of the illumination area 3 (or the slit-shapedbeam 1007) having an illumination distribution substantially resemblingthe Gaussian distribution can also be changed.

A detection area 4 shown in FIG. 37 is an area on the inspection object1 to be inspected by using a TDI image sensor or a CCD image sensor. Inthe case of a TDI image sensor, for example, the dimensions of eachpixel are typically 27 μm×27 μm. The TDI image sensor is typically a64×4,096 CCD image-pickup sensor which comprises 64 rows in the TDI(Time Delay Integration) direction and 4,096 columns in the MUXdirection, and operates in a TDI mode. That is to say, the TDI imagesensors 205 a and 206 a have a configuration comprising n stages of linesensors as shown in FIG. 38 where n is typically 64. A line rate rt isthe amount of information output by the sensor which is the line sensorsin this case. At a line rate rt, accumulated charge is transferredthrough lines 1, 2 and so on, from one line to another. By synchronizingthe movement speed of the y-axis stage 302 for moving the inspectionobject 1 in the direction of the y axis with the line rate rt, an image6 based on a scattered light and a diffraction light generated bytypically an infinitesimal foreign particle 5 is accumulated for a longtime it takes to transfer the charge to the line n so that a defect suchas an infinitesimal foreign particle can be detected with a high degreeof sensitivity. In this image sensor, the image of a defect such as aninfinitesimal foreign particle is detected as a sum of intensities of ascattered light and a diffraction light traveling from the line 1 to theline n. However, a scattered light or a diffraction light coming fromthe same point on the object of inspection and reaching the lines istimewise entirely incoherent.

As described above, a beam emitted by the illumination-light source 101is converted by the illumination optical system (or the radiationoptical system) comprising the components 102 to 104 into a slit-shapedGaussian beam 1007 which is radiated to the surface of the inspectedsubstrate 1 on the stages 301 to 303 typically in a slanting directionto form an illumination area 3 on the surface. While the inspectedsubstrate 1 is being moved in the direction of the y axis by moving they-axis stage 302 in the direction of the y axis, the detectors 205 a and206 a each implemented typically by a TDI image sensor transferselectric charge accumulated in each pixel from one line to another at aline rate rt synchronized with the movement speed of the y-axis stage302. In this way, while an optical image of the detection area 4 on theinspected substrate 1 formed by the detection optical system comprisingthe components 201 to 204 is being picked up, each pixel (or eachdevice) along the width H of the detection area 4 is scanned to generatea detection signal which is then supplied to the image-signal processingunit 400. By processing the detection signal in the image-signalprocessing unit 400, it is possible to detect a defect such as aninfinitesimal foreign particle existing in the detection area 4 with ahigh degree of sensitivity and at a high speed.

By using the TDI image sensors 205 a and 206 a as described above, it ispossible to compute a total of illumination values of a scattered lightor a diffraction light generated by a defect such as an infinitesimalforeign particle where (quantity of light=illumination value×time) and,hence, to increase the sensitivity. In addition, once the slit-shapedbeam 1007 is radiated to the radiation area 3 and, a light generated bythe detection area 4 is received by the TDI image sensors 205 a and 206a while the inspected substrate 1 is being moved in the direction of they axis in synchronization with the line rate rt of the TDI image sensorsso that it is possible to detect a defect such as an infinitesimalforeign particle existing in the detection area 4 with a large width Hat a high speed.

The following description further describes the fourth embodiment of thepresent invention for detecting a defect such as an infinitesimalforeign particle with a size of about 0.1 μm or smaller with a highdegree of sensitivity and at a high speed. That is to say, when it isdesired to detect a defect such as an infinitesimal foreign particlewith a size of about 0.1 μm or smaller with a high degree ofsensitivity, it is necessary to increase the intensity of a scatteredlight or a diffraction light generated by a defect such as aninfinitesimal foreign particle and received by pixels of a TDI imagesensor 302 a and also to reduce the dimensions of each pixel on theinspected substrate 1 to about 1 μm×1 μm or smaller.

It is possible to realize an implementation wherein the dimensions ofeach pixel on the inspected substrate 1 are reduced to about 1 μm×1 μmor smaller as described above by setting the image formationmagnification M of the detection optical system comprising thecomponents 201 to 204 including an objective lens at a value of about 27times or larger for dimensions of each pixel on the TDI image sensors oftypically 27 μm×27 μm. It should be noted that, if 26×4,096 CCD pickupsensors are used as the TDI image sensors 205 a and 206 a, the detectionarea 4 will have a width W not exceeding a value of about 26 μm and aheight H not exceeding a value of about 4,096 μm.

In addition, the detection optical system comprising the components 201to 204 for forming an image in photo-sensitive areas on the TDI imagesensors 205 a and 206 a from an optical image formed by a scatteredlight or a diffraction light generated by the surface of the inspectedsubstrate 1 includes an objective lens having a characteristic which,due to lens aberration, shows the fact that, the farther a position fromthe center of the lens (or the optical axis 2001), that is, the closer aposition to a periphery, the smaller the MTF (Modulation TransferFunction) at the position. The MTF represents changes in contrast of animage of a sinusoidal wave pattern as a function of spatial frequency.For this reason, it is necessary to increase the intensity of ascattered light or a diffraction light generated by pixels 205 ae and206 ae on the edge (or the periphery) with a smallest MTF locatedfarthest from the optical axis 2001 on the photo-sensitive surface ofthe TDI image sensors 205 a and 206 a shown in FIG. 38( a), or generatedby a defect such as an infinitesimal foreign particle located on theedge (or the periphery) with a smallest MTF farthest from the opticalaxis 2001 in the detection area 4 shown in FIG. 37.

By the way, the illumination of the slit-shaped Gaussian beam 1007radiated to the radiation area 3 on the surface of the inspectedsubstrate 1 by the illumination-light source 101 and the illuminationoptical system comprising the components 102 to 104 exhibits theordinary Gaussian distribution as shown in FIG. 37, wasting illuminationoutside the detection area 4. On the other hand, it is necessary toilluminate the illumination area 3 which is made larger than thedetection area 4.

In order to solve this problem, in this present invention, the quantityof a light emitted by the illumination-light source 101 is utilizedeffectively and the illumination on the edge (or the periphery) with asmallest MTF farthest from the optical axis 2001 in the detection area 4is increased most without increasing the illumination of the light inorder to detect a defect such as an infinitesimal foreign particle witha size of about 0.1 μm or smaller with a high degree of sensitivity.That is to say, by employing a low-cost illumination-light source 101for emitting a light with a minimum required illumination, theillumination on the edge (or the periphery) with a smallest MTF farthestfrom the optical axis 2001 in the detection area 4 can be increased mostby the illumination optical system comprising the components 102 to 104to implement illumination with a high degree of efficiency. Examples ofsuch a low-cost illumination-light source 101 are a laser-beam sourcesuch as a semiconductor laser, an argon laser, a YAG-SHG laser or anexima laser and a filament light source such as a canon lamp, anelectric-discharge tube such as mercury lamp and a halogen lamp.

To put it concretely, in the present invention, when theillumination-light source 101 and the illumination optical systemcomprising the components 102 to 104 radiates a slit-shaped beam 1007having an illumination of the Gaussian distribution to illuminate theillumination area 3 on the inspected substrate 1, the illuminationoptical system comprising the components 102 to 104 is adjusted (orcontrolled) to set such a width of the illumination that theillumination on the periphery of the detection area 4 is maximized. TheGaussian distribution of the illumination of the slit-shaped beam 1007shown in FIG. 37 can be expressed by Eq. (6) given below. Theillumination on the periphery of the detection area 4 is maximized whenthe expression on the right-hand side of Eq. (7) is equal to 0.

$\begin{matrix}{{f\left( x_{0} \right)} = {\frac{1}{\sqrt{2\; {\pi\sigma}}}{\exp \left( {{- \frac{1}{2\sigma^{2}}}x_{0}^{2}} \right)}}} & (6) \\{\frac{\partial{f\left( x_{0} \right)}}{\partial\sigma} = {\frac{1}{\sqrt{2\pi}}\left( {- \frac{x_{0}}{\sigma}} \right)\left( {1 + \frac{x_{0}}{\sigma}} \right){\exp \left( {{- \frac{1}{2\sigma \; 2}}x_{0}^{2}} \right)}}} & (7)\end{matrix}$

The maximum illumination f(x0) on the outermost circumference (edge) ofthe detection area 4 in the direction of the x axis corresponding to thephoto-sensitive surfaces of the TDI image sensors 205 a and 206 a isabout 60.7% of the luminance f(0) at the center of the detection area 4.This is because equating the expression on the right-hand side of Eq.(7) to 0 yields x0=σ (for σ=1, x0=1) and substituting σ for x0 in Eq.(6) results in the maximum value f(x0)=0.607f(0). It should be notedthat, for x0=0.8σ to 1.2% in Eq. (6), f(x0)=0.49f(0) to 0.73f(0). Inthis case, for σ=1, x0=0.8 to 1.2 (for the Gaussian beam 1007, areshaping error in the range±20% caused by the illumination opticalsystem comprising the components 102 to 104 is allowable). For σ=0.8×0to 1.2×0 in Eq. (6) which means that, for x0=1, σ=0.8 to 1.2 (for theGaussian beam 1007, a reshaping error in the range±20% caused by theillumination optical system comprising the components 102 to 104 isallowable), f(x0)=0.46f(0) to 0.71f(0). Thus, if a reshaping error ofthe Gaussian beam 1007 in the range±20% caused by the illuminationoptical system comprising the components 102 to 104 is allowable forx0=σ (for σ=1, x0=1), the ratio of the illumination f(x0) on theoutermost circumference (the periphery) of the detection area 4 to theillumination f(0) at the center (the optical axis 2001) of the detectionarea 4 is in the range 0.46 to 0.73, or f(x0)=0.46f(0) to 0.73f(0). Itshould be noted that, if a reshaping error of the Gaussian beam 1007 inthe range±10% caused by the illumination optical system comprising thecomponents 102 to 104 is allowable for x0=σ (for σ=1, x0=1), the ratioof the illumination f(x0) on the outermost circumference (the periphery)of the detection area 4 to the illumination f(0) at the center (theoptical axis 2001) of the detection area 4 is in the range 0.54 to 0.67,or f(x0)=0.54f(0) to 0.67f(0).

In either case, by reshaping a Gaussian beam 1007 by means of theillumination optical system comprising the components 102 to 104 so thatthe ratio of the illumination f(x0) on the outermost circumference (theperiphery) of the detection area 4 to the illumination f(0) at thecenter (the optical axis 2001) of the detection area 4 is set at a valuein the range 0.46 to 0.73, the beam emitted by the illumination-lightsource 101 can be utilized effectively to increase the illumination onthe periphery of the detection area 4 to a value close to a maximum.

FIG. 39 is a diagram showing a graph representing a relation between thewidth of illumination in the direction of the x axis or the standarddeviation σ and the illumination (or the quantity of light per unitarea) f(x0=1) on a circumference (x0=1) in the direction of the x axisin the detection area 4 for a fixed quantity of a light or a fixed totalillumination of a light emitted by the illumination-light source 101.

FIG. 40 is a diagram showing graphs each representing a relation betweenthe coordinate x0 in the direction of the x axis in the detection area 4and the illumination (or the quantity of light per unit area) f(x0) fora fixed quantity of a light or a fixed total illumination of a lightemitted by the illumination-light source 101 with the width ofillumination or the standard deviation σ taken as a parameter. Thefigure shows graphs for parameter values of 0.5, 1 and 2.

As is obvious also from FIGS. 39 and 40, in order to set theillumination on a circumference (x0=1) in the direction of the x axis inthe detection area 4 at a value close to a maximum, the beam is radiatedwith the width σ of the illumination in the direction of the x axisbased on the Gaussian distribution generated by the illumination opticalsystem comprising the components 102 to 104 set at a value of about 1(that is, the standard deviation σ=x0). Let x0 denote the distance fromthe center of the detection area 4 or the optical axis to thecircumference in the direction of the x axis as shown in FIG. 37. Inthis case, if the illumination optical system comprising the components102 to 104 reshapes a light emitted by the illumination-light source 101into a slit-shaped beam 1007 having an illumination of the Gaussiandistribution for a standard distribution σ substantially equal to x0(which is the distance from the center of the detection area 4 or theoptical axis to the circumference in the direction of the x axis asdescribed above) and radiates the beam 1007 to the illumination area 3on the inspected substrate 1, the illumination on a circumference (x0=1)can be maximized. It should be noted that the illumination area 3 is anarea with f equal to at least 0.2×f(0) where the symbol f denotes theillumination on the circumference indicated by Lx and Ly.

It should be noted that, in actuality, TDI image sensors or2-dimensional linear image sensors are used as the detectors 205 and206. In this case, a pixel with a smallest MTF separated farthest fromthe optical axis 2001 is located at a corner of the detection area 4. Inthe case of a TDI image sensor, pixels with a smallest MTF separatedfarthest from the optical axis 2001 are pixels 205 ac and 206 ac locatedat the corners as shown in FIG. 38. Thus, it is desirable to set x0 atthe square root of ((H/2)²+(W/2)²) where the symbols H and Wrespectively denote the width (the length) in the direction of the xaxis and the width in the direction of the y axis of the detection area4 on the inspected substrate 1. If W can be ignored, x0=(H/2). The widthin the direction of the x axis and the width in the direction of the yaxis of a photo-sensitive area (an image-pickup area) on the TDI imagesensor or the 2-dimensional linear image sensor are thus (H×M) and (W×M)respectively. It should be noted that the symbol M denotes themagnification of the image-formation optical system comprising thecomponents 201 to 204.

As described above, by setting the coordinate x0 of the circumference inthe direction of the x axis in the detection area 4 (or in the case of aTDI image sensor or a 2-dimensional linear image sensor, the coordinatex0 of pixels separated farthest from the optical axis 2001) at thesquare root of ((H/2)²÷(W/2)²) or (H/2) and by having the illuminationoptical system comprising the components 102 to 104 reshape a lightemitted by the illumination-light source 101 into a slit-shaped beam1007 having an illumination of the Gaussian distribution for a standarddistribution σ substantially equal to x0 and radiate the beam 1007 tothe illumination area 3 on the inspected substrate 1 where theillumination area 3 is an area with f equal to at least 0.2×f(0) wherethe symbol f denotes the illumination on the circumference indicated byLx and Ly, high-efficiency illumination can be implemented by using alow-cost ordinary illumination-light source 101 without the need toemploy a special illumination-light source with a high power output.Examples of such a low-cost illumination-light source 101 are alaser-beam source such as a semiconductor laser, an argon laser, aYAG-SHG laser or an exima laser and a filament light source such as axenon lamp, an electric-discharge tube such as mercury lamp and ahalogen lamp. As a result, the detection optical system comprising thecomponents 201 to 204 is capable of increasing the intensity of ascattered light or a diffraction light generated by a defect such as aninfinitesimal foreign particle receiving a light radiated to pixels onthe peripheries of the detectors 205 and 206 with a lowest MTF. Thus, adefect such as an infinitesimal foreign particle with a size in therange around 0.1 to 0.5 μm or even an infinitesimal foreign particlewith a size smaller than about 0.1 μm can be detected with a high degreeof sensitivity and at a high speed (or at a high throughput). It shouldbe noted that, even though the illumination in an area in the directionof the x axis varies in dependence on the coordinate x0 as indicated byf(x0)=0.46×f(0) to 0.73×f(0), the inspection object 1 is moved in thedirection of the y axis so that the image-signal processing unit 400compares an image signal with another image signal obtained from thesame pixel array in the direction of the x axis in the detection area 4detected by the detectors 205 and 206 which are each implementedtypically by a TDI image sensor. Thus, there is substantially no effectof the difference in illumination between the center and the periphery.Then, the image-signal processing unit 400 extracts a difference inimage signal between chips or cells which are repeated in the samecircuit pattern on the basis of image signals detected by the detectors205 and 206 each implemented typically by a TDI image sensor while theinspection object 1 is being moved in the direction of the y axis. Bycomparing the extracted difference in image signal using a desiredcriterion, a defect such as a foreign particle can be detected duringthe inspection.

In this case, the fact that the illumination (or the quantity of light)on the periphery of the detection area 4 is increased to a value closeto a maximum is important. In this embodiment, the illumination on theperiphery of the detection area 4 is increased to a value close to amaximum by changing the width of the illumination by means of theillumination optical system comprising the components 102 to 104. As analternative, the illumination on the periphery of the detection area 4is increased to a value close to a maximum by changing the shape of asecondary light source of the illumination by means of the illuminationoptical system comprising the components 102 to 104. As anotheralternative, the illumination on the periphery of the detection area 4is increased to a value close to a maximum by varying the size at thelocation of a Fourier transformation for forming the secondary lightsource.

In addition, since a DUV (deep ultraviolet) laser source is employed asthe illumination-light source 101, it is necessary to use image sensors205 and 206 that are sensitive to a DUV laser. If surface-radiation TDIimage sensors shown in FIG. 41( a) are employed as the image sensors 205and 206, however, an incident light passes through a cover glass 805,gates 801 between metallic films 802 and an oxide film (SiO₂ film) 803before hitting CCDs created on an Si substrate 804. Thus, since anincident light having a small wavelength is attenuated, the sensorbecomes substantially insensitive to a light with a wavelength of 400 nmor smaller. As a result, the DUV light may not be detected. In order tomake the surface-radiation TDI image sensor sensitive to a DUV light,there is provided a technique whereby the thickness of the oxide film803 beneath the gates 801 is reduced so that the amount of attenuationof a light with a small wavelength is decreased. As another technique,the cover glass 805 is coated with an organic thin film. With such anorganic thin film, a visible light is emitted in accordance with anincident DUV light. In this way, the DUV light is detected as a visiblelight by a sensor that is sensitive only to the visible light.

On the other hand, the thickness of the Si substrate 804 is reduced asshown in FIG. 41( b) to provide back-surface-radiation TDI image sensorswhich each receive an incident light hitting the thin Si substrate 804on the rear side as the image sensors 205 and 206. Since an incidentlight hits the surface on the rear side including no gate structure, theDVD quantization efficiency is increased by about 10% or more to give ahigh quantization efficiency and a large dynamic range. As a result, thesensor becomes sensitive to a light having a wavelength of 400 nm orsmaller. In addition, by having the image sensors 205 and 206 go TDI(Time Delay Integration) as described above, the sensitivity can beimproved.

As described above, according to the fourth embodiment, by increasingthe illumination on the periphery of the detection area 4 detected bythe detectors 205 and 206 each implemented by typically a TDI imagesensor to compensate for a decrease in MTF which becomes smaller as thedetected position is separated away from the optical axis 2001 in thedetection optical system comprising the components 201 to 204, theillumination efficiency can be increased. As a result, by employing alow-cost light source such as laser source, it is possible to detect adefect such as an infinitesimal foreign particle with a size in therange around 0.1 to 0.5 μm or even an infinitesimal foreign particlewith a size smaller than about 0.1 μm on an inspected substrate such asan LSI wafer with a high degree of sensitivity and at a high throughput.

In addition, according to the fourth embodiment, an optical image basedon a UVD (deep ultraviolet) laser light such as an exima laser lightobtained from a substrate being inspected is made receivable by a TDIimage sensor so that a defect such as an infinitesimal foreign particlewith a size in the range around 0.1 to 0.5 μm or even an infinitesimalforeign particle with a size smaller than about 0.1 μm on the substratebeing inspected can be detected.

The following description explains the image-signal processing unit 400common to the first to fourth embodiments of the present inventiondescribed above.

There are variations in detection signal received from the detectors 205and 206. Such variations are caused by subtle differences in process forfabricating the device such as an LSI on the actual substrate 1 beinginspected and caused by noise generated during the detection. Forexample, a signal level 73 for a pixel corresponding to a chip 71 isdifferent from a signal level 74 for a pixel corresponding to a chip 72as shown in FIG. 27( a), resulting in a variation. To put it concretely,variations in detection signal for locations 75, 76 and 77 with patternstructures different from each other are also different from each otheras shown in FIG. 27( b). Examples of the locations 75, 76 and 77 withpattern structures different from each other are a memory-cell area, aperipheral-circuit area and an area of another type in the case of amemory LSI. As a result, in a portion with small variations, it ispossible to detect a small defect generating relatively small signalchanges. In a portion with big variations, on the other hand, it ispossible to detect only a large defect generating relatively big signalchanges.

In order to solve the problem described above, the present inventionprovides an image-signal processing unit 400 characterized in that avariation (a standard deviation) among chips is computed for each pixelin the chip and used for setting a threshold value, and a defect such asa foreign particle in an area with a small variation is detected byusing a small threshold value while a defect such as a foreign particlein an area with a big variation is detected by using a large thresholdvalue. In this way, the threshold value for an area with a smallvariation can be reduced without being affected by an area with a bigvariation. An example of an area with a small variation is thememory-cell area in the case of a memory LSI. As a result, it ispossible to detect an infinitesimal foreign particle with a size notexceeding 0.1 μm.

FIG. 28 is a diagram showing a first embodiment implementing theimage-signal processing unit 400. As shown in the figure, the firstembodiment implementing the image-signal processing unit 400 comprises:an A/D converter 401 for converting an analog image signal into digitaldata wherein the analog image signal represents concentration valuesaccumulated for each array of pixels and is obtained synchronously witha movement of the inspected substrate 1 in the direction of the y axisfrom the image sensors 205 and 206 each implemented typically by a TDIimage sensor; a start/stop command circuit 416 for establishing samplingtiming; a data memory 404; a maximum/minimum removing circuit 405 forremoving signals with maximum and minimum levels; a square computingcircuit 406 for computing the square of a signal level s; a signal-levelcomputing circuit 407 for computing the signal level s; a samplecounting circuit 408; a square integrating circuit 409 for integratingsquares of the signal level s; a signal-level integrating circuit 410for integrating values of the signal level s; a sample-count computingcircuit 411 for computing a sample count n by integration; apositive-threshold-value computing circuit (an upper-criterion computingcircuit) 412; a negative-threshold-value computing circuit (alower-criterion computing circuit) 413; a comparison circuit 414 foroutputting a signal used for indicating a defect such as a foreignparticle and obtained as a result of comparison of a detection signaltemporarily stored in the data memory 404 with a positive thresholdvalue computed and set by the positive-threshold-value computing circuit412; a comparison circuit 415 for outputting a signal used forindicating a defect such as a foreign particle and obtained as a resultof comparison of a detection signal temporarily stored in the datamemory 404 with a negative threshold value computed and set by thenegative-threshold-value computing circuit 413; and a detection-resultoutput means 417 for outputting a result of detection comprising: thesignals received from the comparison circuits 414 and 415 to indicate adefect such as a foreign particle; positional coordinates in acoordinate system established for the inspected substrate 1; andinformation on the inspected substrate 1. It should be noted that themaximum/minimum removing circuit 405 is not necessarily required. If themaximum/minimum removing circuit 405 is not employed, all detectedpieces of image data including image data indicating a foreign particleare used in the computation of the threshold values so that thethreshold values can be calculated with a high degree of accuracy and ahigh degree of stability. By using the computed threshold value, on theother hand, it is impossible to detect a foreign particle in an area forwhich the threshold value is computed. It is thus necessary to compute athreshold value for an area to be inspected from signals generated by anarea corresponding to another chip array on the inspected substrate 1.In consequence, since a line for computing a threshold value isdifferent from a line for inspection, the throughput of the inspectionis reduced to a certain degree. Particularly, in the case of a low chipcount, a threshold value can be computed by using image data spread overa plurality of lines. In this case, a data fetch position is specifiedby the start/stop command circuit 416.

The detection-result output means 417 is provided with a CPU forcontrolling the whole defect inspecting apparatus provided by thepresent invention for detecting a defect such as a foreign particle. Thecomponents 406 to 411 are used for finding a variation a of a backgroundsignal for each predetermined area in a chip. The variation a of abackground signal for each predetermined area in a chip is then used bythe positive-threshold-value computing circuit 412 and thenegative-threshold-value computing circuit 413 to set a positivethreshold value TH(H) and a negative threshold value TH(L) respectivelywhich each serve as a criterion for extracting a signal indicating adefect such as a foreign particle. The components 406 to 413 constitutea threshold-value setting circuit 424. On the other hand, the datamemory 404 is used for temporarily storing detected digital imagesignals till threshold values are set by the threshold-value settingcircuit 424. Positional coordinates in a coordinate system establishedfor the inspected substrate 1 are found on the basis of displacements ofthe stages measured by a measurement apparatus not shown in the figureand read signals (scanning signals) output by components such TDI imagesensors with a reference mark on the inspected substrate 1 used as anorigin. Reference numeral 421 denotes another output means fordisplaying the positive threshold value Th(H) showing a variation (astandard deviation σ) typically on a display means. By providing thedisplay means 421, it is possible to form a judgment as to whether ornot a threshold value is correct for each area in a chip while watchingan output for a defect such as a foreign particle extracted from thecomparison circuits 414 and 415.

The detection-result output means 417 may include a display means suchas a CRT, a printing means for printing detection results as a hardcopy, a recording means such as a hard disc, a floppy disc, anphoto-magnetic recording medium, an optical recording medium, an LSImemory or an LSI memory card and a network connected to anotherinspection apparatus, an inspection system or a control system forcontrolling fabrication process equipment or fabrication lines. Inaddition, as described above, the detection-result output means 417 isprovided with a CPU for controlling the whole defect inspectingapparatus provided by the present invention for detecting a defect suchas a foreign particle.

The A/D converter 401 converts signals output by the detectors 205 and206 each implemented typically a TDI image sensor into a digital signalrepresenting a pixel signal. The A/D converter 401 can be placed on thesame substrate as the detection signal processing system 400 or at alocation in close proximity to the detectors 205 and 206 eachimplemented typically a TDI image sensor in the detection optical system200. If the A/D converter 401 is at a location in close proximity to thedetectors 205 and 206, the effect of noise is reduced due todigitization upon transmission but, on the other hand, there is ademerit of an increased number of signal transmission cables.

The following description explains signal processing carried out by thethreshold-value setting circuit 424 with reference to FIG. 27. FIG. 27(a) is a diagram showing a typical layout of chips 71 and 72 and otherdevices on the wafer 1. In most of LSI fabrications, the same chips arecreated on the wafer repetitively. In some cases, a plurality of chips,for example, 2 to 4 chips, are created at the same time at a one-timeexposure. Thus, at the locations of the chips, the same patterns arecreated. As a result, detection signals generated at the positions ofthe chips are naturally identical with each other.

Let notation s (i, j, f, g) denote a signal of a pixel (i, j) in a chip(f, g). As described above, a signal level of a pixel in a chip shouldmatch a signal level of the corresponding pixel in another chip.

In actuality, however, there are variations in pixel detection signal samong chips which are caused by subtle differences among processes butdo not indicate a defect, and noise observed in the detection. Inaddition, even in the same chip, the variation at a location with apattern structure is different from the variation at another locationwith another pattern structure.

The threshold values Th(H) and Th(L) are found from the variation (orthe standard deviation σ(s, f, g)) of the detection signal s(i, j, f, g)between a location in a chip and a corresponding location in anotherchip in accordance with Eq. (8) as follows:

Th(H)=μ(s, f, g)+m1×σ(s(i, j, f, g), f, g)

Th(L)=μ(s, f, g)−m1×σ(s(i, j, f, g), f, g)   (8)

where notations Th(H) and Th(L) denote the positive and negativethreshold values set by the positive-threshold-value computing circuit412 and the negative-threshold-value computing circuit 413 respectivelywhereas notation μ(s, f, g) denotes the average of the values of thesignal for different values of f and g. The average is computed by usingEq. (9) as follows:

μ(s, f, g)=(Σs)/n   (9)

where Σs(i, j, f, g) is computed by the signal-level computing circuit407 for computing the signal level s and the signal-level integratingcircuit 410 for integrating the signal level s whereas n is computed bythe sample counting circuit 408 and the sample-count computing circuit411.

Computed in accordance with Eq. (10) below, σ(s, f, g) is a standarddeviation of the signal s for different values of f and g. ml denotes amultiplier (coefficient).

σ(s, f, g)=√(Σs ² /n−Σs/n   (10)

where Σs(i, j, f, g)² is computed by the square computing circuit 406for computing the square of a signal level s and the square integratingcircuit 409 for integrating the square of the signal level s.

As described above, the threshold values are found by using a valueobtained as a result of multiplication of the standard deviation σ(s, f,g) by a multiplier ml. Normally, it is considered to be desirable to setthe value of the multiplier m1 at about 6. This is because theprobability of generation of a value of at least 6σ is about 1×10⁻¹¹. Atthis probability, the number of pixels detected from a wafer with adiameter of 300 mm for pixel dimensions of 2×2 μm is 7×10¹⁰. Thus, thevalue 6 of the multiplier m1 is found from the fact that areas on theentire surface of the wafer generating detection signals exceeding thethreshold values (or the so-called false information) are statisticallysmaller in size than 1 pixel. Of course, the value of the multiplier m1does not have to be set at 6. In other words, it is needless to say thatanother value can be selected in order to display the effect of thepresent invention. Also from the fact that the number of pieces of falseinformation does not have to be smaller than 1, it is quite within thebounds of possibility that another value of the multiplier m1 can beselected.

FIG. 4 is a diagram showing a second embodiment implementing theimage-signal processing unit 400. The second embodiment is differentfrom the first embodiment in that an image signal of 1 chip is delayedby the data memory 402 and a difference processing circuit 403 extractsa difference in image signal between chips Δs={s(i, j, f, g)−s(i, j,f+1, g)}. Thus, the comparison circuits 414 and 415 extract signals eachindicating a defect such as a foreign particle as a result of comparisonof this differential signal Δs={s(i, j, f, g)−s(i, j, f+1, g)} with theupper threshold value Th(H) and the lower threshold value Th(L)expressed by Eq. (11) below.

Thus, the threshold-value setting circuit comprising the components 406to 413 sets the upper threshold value Th(H) and the lower thresholdvalue Th(L) based on Eq. (11) as follows:

Th(H)=+m1×σ(s(i, j, f, g)−s(i, j, f+1, g), f, g)

Th(L)=−m1×σ(s(i, j, f, g)−s(i, j, f+1, g), f, g)   (11)

It should be noted that the standard deviation σ(Δs, f, g) of thedifferential image between adjacent chips is computed by using Eq. (12)as follows.

σ(Δs, f, g)=√(ΣΔs ² /n−ΣΔs/n   (12)

where τΔs is computed by the signal-level computing circuit 407 forcomputing the signal level Δs and the signal-level integrating circuit410 for integrating the signal level Δs whereas n is computed by thesample counting circuit 408 and the sample-count computing circuit 411.ΣΔs² is computed by the square computing circuit 406 for computing thesquare of a signal level Δs and the square integrating circuit 409 forintegrating the square of the signal level Δs.

By using the differential image Δs between adjacent chips in this way,the standard deviation σ is small even if the detected image signal inthe chip exhibits distribution. As a result, a defect such as a foreignparticle can be detected with a higher degree of sensitivity.

Assume that the process condition varies stage by stage from area toarea starting from the center toward the outermost circumference of awafer. In this case, the signal level also changes stage by stage fromarea to area starting from the center toward the outermost circumferenceof the wafer. As a result, the variation (or the standard deviation σ(s,f, g)) used in the computation of the threshold values based on Eq. (8)increases. However, the difference in signal between only adjacent chips(or the standard deviation σ(Δs, f, g)) is actually not so large as thatused in Eq. (8), making it possible to detect a defect by usingthreshold values which are smaller. Thus, the computations using Eqs.(11) and (12) which are based on the differential value As allowthreshold values of lower levels to be resulted in.

As an improved technique, threshold values can also be computed by usingEq. (13) as follows.

Th=m1×σ(l s(i, j, f, g)−s(i, j, f+1, g)l , f, g)   (13)

where notation Δs denotes the absolute value of the differential signalΔs.

In order to compute threshold values by using Eq. (13), the differenceprocessing circuit 403 is replaced by an absolute-difference processingcircuit 403′ to provide image-signal processing units 400 shown in FIGS.29 and 30. A threshold-value computing circuit 423 computes a thresholdabsolute value Th and a comparison circuit 414 compares the absolutevalue of a differential signal with the threshold value Th to extract asignal indicating a defect such as a foreign particle.

It should be noted that, in this case, the standard deviation σ(Δs, f,g) of a difference in image between adjacent images is computed by usingEq. (14) as follows:

σ(Δsl, f, g)=√(ΣΔs ² /n−ΣΔs/n)   (14)

where ΣΔs is computed by the signal-level computing circuit 407 forcomputing the signal level Δs and the signal-level integrating circuit410 for integrating the signal level Δs.

By the way, in comparison with the third embodiment shown in FIG. 29,the fourth embodiment shown in FIG. 30 has an additional memory positioncontroller 422. The memory position controller 422 specifies coordinatesof the detection signal s or the differential signal Δs on the wafer.That is to say, coordinates of pixels on the wafer, for which a standarddeviation σ between chips is found, can be specified arbitrarily. Inaddition, since coordinates on the wafer can be specified arbitrarily, astandard deviation σ can also be found from areas surrounding targetpixels on chips.

In the case of the third embodiment shown in FIG. 29, positionalcoordinates on the wafer are found from a result of counting the numberof signals. This technique of finding positional coordinates is good fora case in which a standard deviation σ is found from chips laid out on ahorizontal array. However, this technique can not be used to find astandard deviation σ from chips on different arrays.

In order to solve this problem, the memory position controller 422computes positional coordinates of an incoming detection signal s or anincoming differential signal Δs from signals of the stage coordinatesystem and the like which are obtained from the stage controller 305 asis the case with the third embodiment. The computed positionalcoordinates are then supplied to the square integrating circuit 409, thesignal-level integrating circuit 410 and the sample-count computingcircuit 411 which each have a memory function. In this way, dataproduced by the square integrating circuit 409, the signal-levelintegrating circuit 410 and the sample-count computing circuit 411 canbe stored in the storage destination, that is, at the coordinates of thedetection signal With such a configuration, the number of samples forcomputing a standard deviation can be increased even in the case of awafer periphery at which the number of chips on an array is small. As aresult, the threshold-value computing circuit 423 is capable ofcomputing stable threshold values.

By letting the absolute-difference processing circuit 403 compute theabsolute value of a difference as described above, there is exhibited aneffect of, among others, a reduced storage size of the data memory 404since data to be stored therein does not have a sign. In addition, froma result of computation of an absolute value, a calculated standarddeviation σ can be made smaller than a calculation result obtained froma differential value. In order to obtain a generation probability of1×10⁻¹¹, or to get a ‘6σ’ on the normal distribution, a magnification ofabout 10 which is about 1.66 times ‘6’ is required. That is to say, itcan be considered that a calculated standard deviation σ can be reducedto a value equal to 0.6 times a calculation result obtained from adifferential value.

In addition, with this technique, a threshold value for a signal level sis not left, raising a problem in process control and failure analyses.In order to solve this problem, there is provided a circuit 418 forcomputing the level of a threshold value for a position (i, j) in a chipas a threshold-value map as shown in FIGS. 29 and 30. In this circuit418, a threshold-value map is computed from a sum (σ×m1+ΣΔs/n) in whichthe product σ×m1 is calculated by the threshold-value computing circuit423 in accordance with Eq. (14) where the symbol a denotes a standarddeviation and the symbol ml denotes a multiplier, and the average ΣΔs/nof the absolute values of differential signals is computed by theaverage-value computing circuit 425. The result of the computation bythe circuit 418 for each positional data (i, j) computed from thepositions of the stages 301 and 302 as well as the sensors 205 and 206is stored in a threshold-value-map storage means 419 which has a memoryfor each pixel (i, j) on the entire chip. The threshold-value map can bedisplayed on a threshold-value map output means such as a display means421 as requested by the user. In addition, a threshold-value map andoutputs each indicating a defect such as a foreign particle extractedfrom the comparison circuit 414 are also displayed on the display means421, allowing the user to form a judgment as to whether or not thethreshold values are proper. Furthermore, by supplying information ofthe threshold-value map to the detection-result output means 417, it ispossible to output a threshold-value map and pieces of data eachindicating a defect such as a foreign particle extracted from thecomparison circuit 414.

Related to the condition of an underlying layer, the threshold-valuelevel corresponds to information indicating whether or not theunderlying layer is a repetitive-pattern area, an area including aterribly poor spot, a thin-film area or an area with small patterndimensions. It is thus important to analyze which threshold-value levela detected foreign particle has been detected with respect to.Therefore, it will be meaningful to output a threshold value at aposition of a detected foreign particle as data of the detected foreignparticle added to the signal level of the foreign particle by displayingthe threshold value on the display means 421. For this reason, thecomputed threshold-value map is required.

By the way, instead of the signal level s of a foreign particle which is‘a differential value+a threshold value’, it can be considered to be theuse of the differential value Δs.

In addition, as underlying data at the position of a detected foreignparticle, information derived from design data can also be used inaddition to the threshold-value level described above. Examples of suchinformation are information on an area in a chip such as a memory area,a logic-circuit area, a power-supply area and a wireless area. In orderto make such information available, a map of areas in a chip is madefrom the design data, then an information or a phrase being similar tothreshold-value data which is coded from coordinates of the made areamap may be output by being displayed in an operation to display adetected foreign particle.

Furthermore, it is possible to output by displaying underlying area dataof any of the types described above, in the form of a foreign particlemap for each type of underlying data or in the form of a foreignparticle count for each type of underlying data.

As described above, according to the basic concept of the presentinvention, the magnitude of the variation of a signal is found and athreshold value is determined in accordance with the found magnitude ofthe variation of the signal. In a typical configuration of the presentinvention, the threshold-value setting circuit 424 computes a thresholdvalue for each of corresponding pixels in chips from data of the chipsacquired in advance. Threshold values are computed in advance for thesame processes of LSIs of the same type. The computed threshold valuesare typically stored in a threshold-value memory employed in thethreshold-value setting circuit 424 to be compared by the comparisoncircuits 414 and 415 with sequentially incoming signal levels. Data usedin the computation of threshold values can be found once for a lot whichnormally comprises 13 to 25 wafers or found for each wafer.

It should be noted that, in the present invention, since athreshold-value level varies in dependence on the condition of anunderlying layer as described above, the threshold-value levelrepresents the condition of the underlying layer. That is to say, theCPU as an output means 417 is capable of knowing what underlying layer adefect such as a foreign particle exists on or is attached to, providedthat signals each indicating a defect such as a foreign particle areclassified by threshold-value levels obtained from thethreshold-value-map storage means 419. The condition of an underlyinglayer, for example, indicates that the underlying layer is an area withno pattern, an area of cells or an area of peripheral patterns. As analternative, the CPU 417 can be inputted CAD information from a CADsystem by way of an input means 426 which is typically implemented by anetwork or storage media. In this case, the CPU 417 produces area datain a chip like the ones shown in FIGS. 1 and 2 on basis of the inputtedCAD information and is capable of further knowing directly the conditionof an underlying layer being existed a defect such as a foreign particleby using the area data in a chip.

The technique of inferring the condition of an underlying layer from asignal level or a threshold-value level of the underlying layer withoutusing area data exhibits an effect that it is not necessary to set areasin a chip in advance. In this case, the CPU 417 is capable ofclassifying signal levels of the underlying layer as areas such as cellunits from the magnitudes of threshold-value levels of the entire chipfound once from a threshold-value map stored in threshold-value-mapstorage means 419. In this case, a judgment for an area can be formed bycomparing the threshold-value level with a difference Δs in signal levelbetween adjacent chips or the signal level itself. After knowing thecondition of the underlying layer, the CPU 417 is capable of detecting,outputting and controlling a defect or a foreign particle only, forexample, on a cell unit.

Next, a fifth embodiment implementing the central processing unit 400 isexplained by referring to FIG. 31. The fifth embodiment computes adifference Δs in detection signals (or data) between adjacent chips andthen finds a variation (or a standard deviation σ(Δs, f, g)) of datasurrounding a target pixel.

The fifth embodiment includes delay memories 425 and 426 and a windowopening circuit 427 to form the so-called pipeline processing system.Components 406 to 413 compute the variation σ(Δs, f, g) from peripherypixels' differential values Δs(i+1, j+1, f, g), Δs(i+1, j, f, g),Δs(i+1, j−1, f, g), Δs(i, j−1, f, g), Δs(i−1, j−1, f, g), Δs(i−1, j, f,g), Δs(i−1, j+1, f, g) and Δs(i, j+1, f, g) of a window excluding acentral differential value Δs(i, j, f, g) of the window in accordancewith Eq. (15) given below. Then, the threshold values Th(H) and Th(L)are computed in the basis of the computed standard deviation σ.

σ(Δs, f, g)=√(ΣΔs ²/8−ΣΔs/8)   (15)

The comparison means 414 and 415 compare the central differential valueΔs(i, j, f, g) of the window cited above with the computed thresholdvalues Th(H) and Th(L) respectively to extract a defect such as aforeign particle. The dimensions of the window do not have to be 3×3 asshown in the figure. Instead, they can be 4×4, 5×5 or 7×7. As analternative, the computation can be applied to a plurality of windowsizes. In addition, the object of inspection is not necessarily thecentral differential value. Instead, the object of inspection can be anydifferential value in the window. As another alternative, the object ofinspection can be another value such as an average or a sum ofdifferential values of a plurality of pixels on the window. The size ofthe window should be determined in accordance with the size of a foreignparticle to be detected or the shape of a background pattern.

The following description explains a sixth embodiment implementing thecentral processing unit 400 wherein a threshold value of the absolutesensitivity is set. By setting a threshold value of the absolutesensitivity based on Eq. (13) given above, the control size of a foreignparticle or a defeat in LSI fabrication processes can be made uniformfor all the processes.

The CPU 417 of the detection signal processing circuit 400 corrects asignal level or preferably a differential signal level ss which isreceived as a result of detection in addition to coordinates of aforeign particle.

To put it concretely, the differential signal level ss is corrected intoa differential signal level ss′ in accordance with Eq. (16) as follows:

ss′=ss/(P1×ND×k×rb×k(t))   (16)

where the symbol P1 denotes the power of a laser generated duringinspection, the symbol ND denotes the ND of the ND filter expressed interms of %, the symbol k denotes a constant indicating whether or not apolarization plane exists, the symbol rb denotes the reflectance of theunderlying layer and the symbol k(t) denotes a correction coefficientdependent on the thickness t of the oxide film. A value of 1 of theconstant k indicates that a polarization plane exists while the constantk is desirably set at around 10 to indicate that a polarization planedoes not exist. It should be noted that, since the laser power P1exhibits a distribution characteristic P1(x) known as the so-calledshading over illumination positions along the x axis, the value of P1(x)can be substituted for P1 in Eq. (16) to give a better result.

The size d of a foreign particle or a defect is a function df(ss) ofdifferential signal level ss obtained in advance. In actuality, the sized of a foreign particle or a defect displayed on the display means 421is found by substituting the corrected differential signal level ss′ forthe differential signal level ss in the function df(ss) as follows:

d=df(ss′)   (17)

In particular, for a small foreign particle, according to Mie'sscattering theory, the corrected differential signal level ss′ isproportional to the (−6)th power of the size d of the foreign particle.Thus, the size d of the foreign particle can also be found from thisproportional relation.

The following description explains an embodiment implementing thecentral processing unit 400 wherein a judgment on the existence of adefect is based on a high S/N ratio for of course an infinitesimalforeign particle and a large foreign particle having a spreading shape.By the way, it is necessary not only to detect an infinitesimal foreignparticle but also not to miss a large foreign particle or a foreignparticle having a thin-film shape spread over a range of several micronsby using the comparison circuits 414 and 415 employed in the centralprocessing unit 400 for forming a judgment on the existence of a defect.Since a high-level detection signal is not always generated by such alarge foreign particle, however, the S/N ratio of a detection signal ofa pixel unit is low, causing such a large foreign particle to beneglected.

Let the symbol S denotes an average detection signal level of 1 pixeland notation σ/n denotes an average variation. By convolution for anextracted unit having dimensions of n pixels×n pixels which correspondto the size of a large foreign particle, the level of the detectionsignal is found to be n²S, the variation is found to be nσ and the S/Nratio is found to be nS/σ. If a large foreign particle is detected inpixel units, on the other hand, the level of the detection signal isfound to be S, the variation is found to be σ and the S/N ratio is foundto be S/σ. Thus, by convolution for an extracted unit having dimensionsof n pixels×n pixels which correspond to the size of a large foreignparticle, the S/N ratio is increased by n times.

As for an infinitesimal foreign particle with a size of about 1 pixel,the level of a detection signal detected for a 1-pixel unit is found tobe S, the variation is found to be σ and the S/N ratio is found to beS/σ. By convolution for an extracted unit having dimensions of npixels×n pixels in the case of an infinitesimal foreign particle with asize of about 1 pixel, on the other hand, the level of the detectionsignal is found to be S/n², the variation is found to be nσ and the S/Nratio is found to be S/nσ. Thus, for an infinitesimal foreign particlewith a size of about 1 pixel, by keeping the signal of a pixel unit asit is, the S/N ratio can be increased.

It is thus obvious from the description given above that, by convolutionof an image signal obtained from the data memory 404 for each extractedoperator 520, a gray scale image signal with different levels is outputfrom pixels at the center. There are a plurality of operators 520 withdifferent dimensions expressed in terms of pixel units for detection ofa defect. As shown in FIG. 52, examples of the operators 520 are anoperator 521 extracted as 1 pixel unit, an operator 522 extracted as aunit of 3 pixels×3 pixels, an operator 523 extracted as a unit of 4pixels×4 pixels, an operator 524 extracted as a unit of 5 pixels×5pixels and an operator 525 extracted as a unit of n pixels×n pixels. Inthis case, the levels of the gray scale image signal are S, 9S, 16S, 25Sand n²S for the operators 521, 522, 523, 524 and 525 respectively wherethe symbol S denotes an average detection signal level of 1 pixel. Onthe other hand, multiplication circuits 541, 542, 543 and 544 multiply athreshold value m1×σ output by a threshold-value circuit 423 employed inthe threshold-value setting circuit 424 by approximation threshold-valuecoefficients 3, 4, 5 and n respectively. These approximationthreshold-value coefficients 3, 4, 5 and n are inferred from the centrallimit theorem. Comparison circuits 531, 532, 533, 534 and 535 constitutea comparator 414′. In the comparison circuit 531, the gray scale imagesignal obtained as a result of the convolution at the operator 521 iscompared with the threshold value m1×σ in order to form a judgment onthe existence of a defect such as a foreign particle and to output asignal indicating a foreign particle in accordance with the outcome ofthe judgment. In the comparison circuit 532, on the other hand, the grayscale image signal obtained as a result of the convolution at theoperator 522 is compared with a threshold value obtained as a product ofthe threshold value m1×σ and the approximation threshold-valuecoefficient 3 in order to form a judgment on the existence of a defectsuch as a foreign particle and to output a signal indicating a foreignparticle in accordance with the outcome of the judgment. Likewise, inthe comparison circuit 533, the gray scale image signal obtained as aresult of the convolution at the operator 523 is compared with athreshold value obtained as a product of the threshold value m1× and theapproximation threshold-value coefficient 4 in order to form a judgmenton the existence of a defect such as a foreign particle and to output asignal indicating a foreign particle in accordance with the outcome ofthe judgment. Similarly, in the comparison circuit 534, the gray scaleimage signal obtained as a result of the convolution at the operator 524is compared with a threshold value obtained as a product of thethreshold value m1×σ and the approximation threshold-value coefficient 5in order to form a judgment on the existence of a defect such as aforeign particle and to output a signal indicating a foreign particle inaccordance with the outcome of the judgment. Similarly, in thecomparison circuit 535, the gray scale image signal obtained as a resultof the convolution at the operator 525 is compared with a thresholdvalue obtained as a product of the threshold value m1×σ and theapproximation threshold-value coefficient n in order to form a judgmenton the existence of a defect such as a foreign particle and to output asignal indicating a foreign particle in accordance with the outcome ofthe judgment. That is to say, the comparison circuit 531 detects aninfinitesimal foreign particle with a size of about 1 pixel. On theother hand, the comparison circuit 532 detects a foreign particle withdimensions of about 3 pixels×3 pixels. Similarly, the comparison circuit533 detects a foreign particle with dimensions of about 4 pixels×4pixels. Likewise, the comparison circuit 534 detects a foreign particlewith dimensions of about 5 pixels×5 pixels. Similarly, the comparisoncircuit 535 detects a foreign particle with dimensions of about npixels×n pixels. A logical-sum circuit 550 computes a logical sum of thesignals output by the comparison circuits 531 to 535 each to indicate aforeign particle. Thus, signals indicating foreign particles withdifferent dimensions can be detected each at a high S/N ratio. As aresult, the degree of complementation can be raised for a large foreignparticle generating a low detection-signal level and having a spreadshape.

It should be noted that, by providing operators with differentdimensions expressed in terms of pixels for forming a judgment on theexistence of a defect such as a foreign particle after the differenceprocessing circuit 403′ and a pixel signal is integrated to generate anoutput each time the dimensions expressed in terms of pixels arechanged, the comparator 414 is made capable of detecting a signalindicating a foreign particle with a size matching the changeddimensions expressed in terms of pixels. In this case, however, it isnecessary to carry out the inspection a plurality of times by changingthe dimensions expressed in terms of pixels. Nevertheless, an accuratevalue is set as a threshold value. In addition, if operators withdifferent dimensions expressed in terms of pixels for forming a judgmenton the existence of a defect such as a foreign particle are providedafter the difference processing circuit 403′, an image memory 404 with astorage capacity increased by a plurality of times is required. However,it is not necessary to provide more than one threshold-setting circuit424. In addition, a threshold value m1×σ output by a threshold-valuecircuit 423 employed in the threshold-value setting circuit 424 can bemultiplied by an approximation threshold-value coefficient to find afinal threshold value.

As described above, by adjusting dimensions expressed in terms of pixelsfor formation of a judgment on the existence of a defect such as aforeign particle by integration or convolution of a rectangular functionto the size of a foreign particle to be detected in the comparator 414′,it is possible to catch a large foreign particle generating a lowdetection-signal level and having a spread shape.

The next description explains embodiments implementing a technique ofspecifying conditions adopted in the defect inspecting apparatusprovided by the present invention for detecting a defect such as aforeign particle by referring to FIGS. 42 to 46. FIG. 42 is a diagramshowing a sequence of specifying conditions followed by the defectinspecting apparatus provided by the present invention for detecting adefect such as a foreign particle. Inspection of a substrate for adefect is carried out under conditions set in this sequence.

As shown in FIG. 42, the sequence begins with a step S41 at which theCPU 417 displays a screen for selecting one of a variety of modes likeones shown in FIG. 43 on the display means 421. By using an input means426 such as a keyboard or a mouse, the user is allowed to select an itemin each mode. Typical modes include a chip matrix S411 on a wafer, acondition specifying mode S412 and a threshold-value advance selectionmode S413. Selectable items of the chip matrix S411 are items related tochip layout data such as the size of the chip, the start coordinates ofthe chip and information indicating non-existence of a chip. As shown inFIG. 43, selectable items of the condition specifying mode S412 are: a.Area priority; b. Standard; c. Sensitivity priority; and d.Post-sensitivity-display selection. On the other hand, selectable itemsof the threshold-value advance selection mode S413 are: a. m1=6:False-information generation rate of 00%; b. m1=10: False-informationgeneration rate of 00%; and c. m1=15: False-information generation rateof 00%.

The ‘a. Area priority’ of the condition specifying mode S411 is aninspection-condition mode which allows a relatively large foreignparticle in an area larger than the standard mode to be detected bytypically weakening the power of the illumination beam. An area with asaturated background level is virtually an uninspectable area. In thearea-priority mode, however, the size of an uninspectable area can bemade 5% or smaller. FIG. 45 is a diagram showing a case in which thearea-priority mode allows a foreign particle having a size of about 2.5μm to be detected from the entire area.

The ‘b. Standard’ of the condition specifying mode S412 is aninspection-condition mode which allows a foreign particle to be detectedat a standard sensitivity. FIG. 45 is a diagram showing a case in whichthe standard mode allows a foreign particle having a size of about 1.0μm to be detected from about 90% of the entire inspection area andfurthermore to a foreign particle having a size of about 0.2 μm to bedetected.

The ‘c. Sensitivity priority’ of the condition specifying mode S412 is amode with the sensitivity set at such a high value that a foreignparticle more infinitesimal than that of the standard mode can bedetected, or an inspection-condition mode set to allow a specifieddetection sensitivity to be preserved. FIG. 45 is a diagram showing acase in which the sensitivity-priority mode allows a foreign particlehaving a size of about 0.5 μm to be detected from about 75% of theentire inspection area and furthermore to a foreign particle having asize of 0.1 μm to be detected. To put it concretely, by increasing thepower of the illumination light, the power of the illumination light isset at a level capable of assuring an inspection condition allowing aforeign particle smaller in size than a foreign particle indicated by aspecified detection size or assuring a specified detection sensitivity.In the examples shown in FIG. 45, the inspection condition allows aforeign particle having a size of about 0.1 μm to be detected or thespecified detection sensitivity allows a foreign particle having a sizeof about 0.5 μm to be detected from at least 75% of the inspection area.

The ‘d. Post-sensitivity-display selection’ of the condition specifyingmode S412 is a mode displaying results of inspection obtained in one ofthe 3 modes described above, or a map of threshold values in a chip or arelation between the size (the sensitivity corresponding to thethreshold value) and the inspection area (a threshold-value histogram)and allowing the user to select an appropriate item among what aredisplayed.

In the area-priority mode, the power of the illumination light is lowestand the dynamic range is wide. When the defect inspecting apparatus isswitched from the area-priority mode to the standard mode, the power ofthe illumination light is increased while the dynamic range is reduced.The same holds true when the defect inspecting apparatus is switchedfrom the standard mode to the sensitivity-priority mode. Thus, in thecase of the area-priority mode, in the threshold-value map, there areonly few uninspectable areas from which a foreign particle can not bedetected, but only foreign particles with a size of up to about 0.5 μmcan be detected. In the standard mode, there are many saturateduninspectable areas from which a foreign particle shown in a white colorin FIG. 45 can not be detected. However, foreign particles with a sizeof up to about 0.2 μm can be detected. In the case of thesensitivity-priority mode, there are even more saturated uninspectableareas from which a foreign particle shown in a white color in FIG. 45can not be detected. However, foreign particles with a size of up toabout 0.1 μm can be detected. In the threshold-value histograms,reference numeral 471 denotes a relation between the sensitivity and theinspection area rate, whereas reference numeral 472 denotes a relationbetween the sensitivity and the integration value of the inspectionarea. It should be noted that a threshold-value histogram can also showonly one of the relations 471 and 472.

An item in the threshold-value advance selection mode S413 can beselected in accordance with an allowable probability of generation offalse information by checking this allowable probability with thedisplayed probabilities of generation of false information (thegeneration frequencies) 00%. This is because, as described earlier,since a threshold value is set from the variation a of the level of adetected image-picture signal, the probability of generation of falseinformation 00% can be automatically computed for a display from themultiplier m1 on the basis of the theory of statistics. Thus, thethreshold value setting and the multiplier m1 for the probability ofgeneration of false information can be displayed with ease.

The CPU 417 then goes on to the next step S42 of the flow of thesequence shown in FIG. 42. At the step S42, the spatial filter 202 isset either manually or automatically in accordance with the structure ofa circuit pattern on a selected wafer. The CPU 417 then proceeds to astep S43 at which an image formed by the spatial filter 202 is confirmedeither by visual observation or automatically by using an image formedby a TV camera 228 and the image-formation optical system 227, a focusof which is adjusted to the position of the filter as shown in FIG. 46.If the image is not confirmed, the CPU 417 then goes back to the stepS42 to again set the spatial filter 202. If the image is confirmed, onthe other hand, the CPU 417 goes on to the next step. The spatial filter202 has a configuration wherein the pitch and the phase of its opticalshielding pattern can be changed. As shown in FIG. 46, a single assembly225 comprises a beam splitter 204 and a spatial-filter observationoptical system which comprises a half mirror 226, the image-formationlens 227 and the TV camera 228. The internal structure of the assembly225 can be changed as shown by an arrow 230. To be more specific, in anoperation to detect an ordinary foreign particle, the beam splitter 204is placed on the detection optical axis 204. In a spatial-filterobservation, on the other hand, it is the half mirror 226 that is placedon the detection optical axis. In an automatic operation, by subjectinga diffraction light and an optical shielding pattern detected in theaperture 20 a to an image-pickup operation carried out by the TV camera228 in the same way as that shown in FIG. 19( b), the pitch and thephase of the optical shielding pattern can be adjusted so that thediffraction light is shield ed. In addition, by shifting the position ofthe TV camera 228 in a direction indicated by an arrow 229 in FIG. 46,it is also possible to adjust the directivity of the optical shieldingpattern while observing also the image of a circuit pattern on thesubstrate being inspected.

Then, the flow of the sequence goes on to a step S44 at which the CPU417 inputs a value of the magnification (coefficient) m1 in the rangearound 6 to 15 for the standard deviation σ for setting a thresholdvalue Th from the input means 426. The flow of the sequence then goes onto a step S45 at which the CPU 417 inputs a detection size of a foreignparticle from the input means 426 in size specification S451. Thedetection size of a foreign particle is used for computing a laser powerwhich can be used to detect a foreign particle having the specifiedsize. The laser-beam source 101 is then controlled by a control signal430 to generate a laser beam having the computed laser power.

Then, the CPU 417 goes on to a step S46 at which, in order to setthreshold values for a partial area or the entire area of a chip, thewafer is scanned and inspected and a threshold-value map computed by thethreshold-value computing means 418 is stored in the threshold-value-mapstorage means 419. Then, the threshold-value map (or a threshold-valueimage) like the one shown in FIG. 44 or threshold-value histograms likethe ones shown in FIG. 45 are displayed on the display means 421. Thehistograms shown in FIG. 45 each represent a relation between thesensitivity and the inspection area having the sensitivity with thesensitivity represented typically by the horizontal axis. Each of thehistograms shown in FIG. 45 also represents a relation between thesensitivity and the integration value of the inspection area. The useris then allowed to check the sensitivity on the basis of typically thedisplayed threshold-value map to confirm whether the threshold value isat a desired level (the size of a foreign particle to be detected). Ifsuch a threshold value is not confirmed, the flow of the sequence goesback to the step S45. If such a threshold value is confirmed, on theother hand, the flow of the sequence goes on to the next step S47.

As described above, the CPU 417 goes on to the step S47 at which theentire area of the wafer is inspected. If an area generating falseinformation exists, such an area may be set as a non-inspection area (aninhibit area) on the basis of CAD information in the chip or informationincluded in the threshold-value map. The flow of the sequence then goeson to a step S48 at which the CPU 417 issues a command to inspect thesubstrate 1 for a defect such as a foreign particle. If the centralprocessing unit 400 determines that a defect such as a foreign particleexists, the level of the detection signal and detection coordinates ofthe defect are stored in a storage unit 427.

Finally, the flow of the sequence goes on to a step S49 at which theactual inspected substrate 1 is optically observed by using anoptical-observation microscope 700 implemented typically by anultraviolet-ray microscope or a common-focus microscope installedbesides the defect inspecting apparatus in order to confirm whether aresult of the inspection indicates a defect such as a foreign particleor is false information. With this confirmation, it is possible toconfirm whether a condition specification has been set properly for thefirst time. In particular, if an area including an infinitesimal andcomplicated circuit pattern coexists with an area causing colornonuniformity in a chip on the inspected substrate 1, it is necessary tofinally confirm the condition specification by using theoptical-observation microscope 700. If the result of the confirmation offalse information done at the step S49 is NO, the flow of the sequencegoes on to a step S50 at which the magnification (coefficient) m1 forsetting a threshold value is increased or decreased in some cases. Theflow of the sequence then goes back to the step S45 at which the laserpower is changed if necessary. In the case of a YES result, on the otherhand, the condition specifying sequence is ended.

It should be noted that the objective can be achieved even if only partof the procedure described above is adopted or if the flow of thesequence is changed.

As described above, it is possible to specify conditions optimum for adesired size (sensitivity) of a foreign particle with ease and within ashort period of time.

It should be noted that, in the optical observation carried out at thestep S49, the detected foreign particle (including that falseinformation) on the inspected substrate 1 can be moved to the positionof a detection optical system 701 employed in the optical-observationmicroscope 700 shown in FIG. 46 by moving the stages 301 and 302 so asto allow the inspector to observe the image thereof. In the case of thedetection optical system 200, the image-formation optical subsystemthereof has a high resolution and, in addition, coordinates of a pointof observation are changed during a movement of the object of inspectionwith a high degree of precision. In particular, the dark-visual-fieldillumination optical system comprising the components 102 to 105 allowsa foreign particle with a size-smaller than the resolution limit of thedetection optical system 200 to be detected. Thus, with an ordinarymicroscope, observation is impossible in many cases. For this reason,the optical-observation microscope 700 is employed. As theoptical-observation microscope 700, it is desirable to employ typicallya common-focus optical system with an extremely high resolution or anoptical system with a short wave illumination light such as ultravioletrays or deep ultraviolet rays with a typical wavelength of 248 nm, 365nm or 266 nm or a wavelength close thereto. That is to say, for awavelength of about 200 nm, the optical-observation microscope 700 iscapable of producing an image close to an image formed by an electronmicroscope as well as allows the size of a defect such as a foreignparticle to be found with a high degree of precision attributesincluding shapes of defects such as foreign particles to be classified.It should be noted that FIG. 46 shows the configuration of theoptical-observation microscope 700. As shown in FIG. 41, theoptical-observation microscope 700 comprises: the aforementioneddetection optical system 701 having a bright-visual-field ordark-visual-field ultraviolet-ray illumination optical subsystem and aTDI image sensor of FIG. 41 capable of detecting an ultraviolet ray; animage-signal processing unit 702 for carrying out processing such as A/Dconversion of an image detected by the TDI image sensor of the detectionoptical system 701; an image memory 704 for storing an image completingthe A/D conversion in the image-signal processing unit 702 at an addressbased on coordinate data of a foreign particle (or that considered to befalse information) detected by the central processing unit 400; and adisplay means 703 for displaying an image. Thus, by controlling thestages 301 and 302 in accordance with coordinate data of a foreignparticle (or that considered to be false information) detected by thecentral processing unit 400 to display an image considered to be falseinformation on the display means 703 for observation by the inspector,the inspector is capable of confirming the false information by usingthe optical-observation microscope 700. To put it in detail, the stages301 and 302 are moved to take the position indicated by detectioncoordinates stored in the storage unit 427 to the visual field of theoptical-observation microscope 700, and the optical-observationmicroscope 700 detects an image in the visual field and displays on thedisplay means 703 or stores the image in the image memory 704 asnumerical image data. This stored data can be redisplayed whennecessary. In addition, data stored in the image memory 704 can besupplied to the CPU 417 of the central processing unit 400 and observedlater along with image data transferred from another defect inspectingapparatus. Anyway, as the optical-observation optical system 700, abright-visual-field microscope having a high resolution, adark-visual-field microscope having the illumination optical system 100described above, a dark-visual-field microscope having incoherentillumination, a phase-differential microscope or a common-focusmicroscope can be employed.

In the condition specifying sequence described above, the specificationof conditions can be completed by merely making a chip matrix at thestep S41 and entering the size of a foreign particle to be detected atthe step S45. That is to say, a chip matrix and the size of a foreignparticle (or a sensitivity corresponding to the size of a foreignparticle) are conditions that absolutely need to be specified.

In other words, the confirmation of the filter at the step S43, thesetting of the multiplier m1 at the step S44, the confirmation of asensitivity at the step S46, the setting of an inhibit area (anon-inspection area) at the step S47 and the confirmation of falseinformation at the step S49 are optional condition setting steps.

In addition, in setting of a threshold value, the use of a thresholdvalue on the stable side (a large threshold value) suppresses generationof false information. By decreasing the threshold value, on the otherhand, a foreign particle can be detected with a high degree ofsensitivity even if false information is generated to a certain degree.The former technique is suitable for quality control of a waferprocessing apparatus and therefore used for detecting an abnormality.The latter technique is on the other hand suitable for an analysis of astate of generation of a failure and a defect, and thus used forclassifying defects and foreign particles in determining a cause ofgeneration of a failure.

The following description explains inference of the diameter of aforeign particle carried out by the CPU 417 from a scattered-light imagestored in the image memory 404 as a result of processing comprisingdetection by the image sensors 205 and 206 and A/D conversion by theA/D-conversion unit 401 by referring to FIG. 47. The level of a signalrepresenting a scattered light or, the more desirable differential valuess, varies in accordance with the size of a particle or a defect such asan injury which generates the scattered light. The CPU 417 corrects thedetection signal ss by multiplying the signal ss by a correctioncoefficient k(t) to produce a corrected detection signal ss′. In thiscase, the correction coefficient k(t) is calculated in accordance withconditions including the power of the laser beam, the polarization plane208 on the inspection, the spatial filter 202 and the illuminationangles Φ1 and α1 in such a way that the corrected detection signal ss′can be made representative of the size d of an external material or adefect such as an injury. The CPU 417 uses information on the size of aforeign particle or a defect calculated in this way as a size to benormally specified in the detection-size specification at the step S45of the condition specifying sequence described earlier.

As described earlier, an image representing a foreign particle isdetected by the TDI image sensors 205 a and 206 a and stored in theimage memory 404. A relation between the size of the image (or thenumber of pixels showing the spread of the image of the foreignparticle) and the dimensions of the foreign particle exhibits a certaintrend as shown in FIG. 47. Thus, the CPU 417 is capable of inferring thediameter of the foreign particle by computing the number of pixelsshowing the foreign particle with such pixels obtained from a detectedimage stored in the image memory 404. Particularly, in the case of aforeign particle having a size in the range around 0.13 to 0.2 μm, acorrelation between the size and the dimensions of the image of theforeign particle can be found out. As a result, the size of a foreignparticle or the diameter of a foreign particle can be inferred.

In addition, in the case of a foreign particle size accommodatable inone pixel and a signal level exceeding the dynamic range of the imagesensors 205 and 206, the size of the foreign particle can be inferred byusing the following technique. Even if the size of a foreign particlecan be accommodated in one pixel, an image exhibiting a spread as shownin FIG. 48( a) is formed. From the width between the rise and the fallof this spread, that is, from the width W of the threshold value, theintensity of a signal exceeding a peak level or the dynamic range can beinferred. In this case, as shown in FIG. 48( b), the surface conditionof the cover glasses 220 of the image sensors 205 and 206 is set at aspecific surface roughness to let the cover glasses 220 cause scatteringand produce a spreading forcibly. In this way, the size of a foreignparticle can be inferred more easily from a detection image.

Next, a plurality of inspections by the defect inspecting apparatusprovided by the present invention are explained. In the inspections, inorder to provide a dynamic range, for example, the surface of theinspected substrate 1 is inspected in the area-priority mode, thestandard mode and the sensitivity-priority mode, that is, under acondition of an increasing power of the illumination light, and in thestandard mode or in a condition of a reduced power of the illuminationlight. Results of the inspections are then supplied to the CPU 417. Theresults of the inspections can be simply integrated into aninspection-result map. The inspection-result map is a drawing showingplotted defect marks at positional coordinates at which defects such asforeign particles have been detected. The CPU 417 may also produce alist of coordinates of foreign particles or a list/map showingdetection-signal levels of foreign particles in place of such aninspection-result map.

In addition, a plurality of inspections are carried out not only toprovide a dynamic range, but carried out also in order to allowdetection of a defect such as an infinitesimal injury or foreignparticle by changing typically the travel times of the stages 301 and302. Furthermore, the inspections are also carried out by changingconditions such as the directions α1, Φ1 (including 0) and Φ2 (including0) of the illumination set by the illumination optical system 100, thepresence/absence of the polarization plane 208 and the use of thewhite-color illumination 500 and the laser illumination 100.

In addition, as a technique of processing adopted by the CPU 417, thecorrected detection-signal level ss′ of a defect detected under aplurality of inspection conditions is mapped onto a space of multidimensions such as the power of the illumination light, the illuminationdirections, the presence/absence of the polarization plane, thewhite-color illumination and the laser illumination to produceclassified results from a distance in the space with the class portionseparated. For example, as shown in FIG. 49, curves are each plotted toshow a relation between the level ss′ of a detection signal produced bythe laser-illumination optical system 100 on the x axis and the levelss′ of a detection signal produced by another illumination opticalsystem such as the white-color illumination system 500 and theillumination system shown in FIG. 50 on the y axis. The curves areplotted in 2 areas separated by a straight line represented by y=βx setin advance. The classification of the relations into these 2 areasallows a characteristic of a defect to be identified. As describedabove, the illumination system shown in FIG. 50 can be used as anotherillumination system. In this case, results of experiments have verifiedthat a defect such as a foreign particle with a relation thereof plottedin the area represented by y>βx is an injury or a flat foreign particle491 which is not much illuminated by an illumination light in a slantingdirection. On the other hand, a defect such as a foreign particle with arelation thereof plotted in the area represented by y<βx is a foreignparticle 492 with a relatively large height. The boundary line betweenthe 2 areas does not have to be a straight line. That is to say, theboundary line can also be a curve for example. As a matter of fact, aplurality of straight and/or curved lines can serve as boundariesbetween areas. In addition, a space for finding these distances can havea plurality of dimensions. Further, these inspections can be carried outby using the detectors 205 and 206 at the same time.

Instead of radiating the laser beams 10, 11 and 12 as shown in FIG. 3 inslanting illumination directions, the illumination system shown in FIG.50 radiates a laser beam 3 to the inspected substrate 1 in a directionsubstantially perpendicular to the surface of the substrate 1 byreflecting the laser beam 10 using a straight-line-shaped fine mirror240 which is inserted between the objective lens 201 and the inspectedsubstrate 1. Thus, a 0th-order diffraction light (a regularly reflectedlight) is shield ed by the straight-line-shaped fine mirror 240 while afirst-order diffraction light and higher-order diffraction lights passthrough the objective lens 201. Note that it is desirable to design thestraight-line-shaped fine mirror 240 into a band of a sufficiently finestraight-line shape so that, on the surface of the spatial filter 202,the functions of the spatial filter 202 can be executed.

Next, connection of the defect inspecting apparatus provided by thepresent invention to external equipment is explained. As describedabove, the CPU 471 controls the entire defect inspecting apparatusprovided by the present invention. For this reason, data such as resultsof inspection and conditions for inspection such as particularly athreshold-value map is stored in the storage unit 427 connected to theCPU 417. It is also desirable to communicate the results of inspectionand conditions for inspection stored in the storage unit 427 to anothercomputer through a local area network 428 or a modem. In particular, byconnecting the defect inspecting apparatus to the Internet, informationsuch as improvements of the conditions for inspection and states ofproblems encountered in the defect inspecting apparatus can be exchangedbetween the user utilizing the defect inspecting apparatus and themanufacturer of the apparatus. If information exchanged between the userand the manufacturer of the defect inspecting apparatus is encrypted byusing an encryption key known by both the user and the manufacturer,security of data can be protected. In addition, information such asimprovements of the conditions for processing and states of problemsencountered in the processing apparatus based on results of inspectionof substrate for a defect such as a foreign particle produced by thedefect inspecting apparatus can also be exchanged between the userutilizing the processing apparatus and the manufacturer of theapparatus.

Further, by designing the image-signal processing unit 400 as aprogrammable system, algorithms adopted by the units 400 shown in FIGS.4, 28, 29, 30 and 31 can each be implemented as a program which can beexecuted by the system. These algorithms each keep up with partialfluctuations in signal intensity caused by interference of typically anoxide film on the surface of a wafer. It is thus possible to implementan algorithm for dealing with the so-called color irregularities.

The following description explains lines and methods using the defectinspecting apparatus provided by the present invention as described sofar to fabricate semiconductors by referring to FIGS. 32 to 34.

As shown in FIG. 32, a line using the defect inspecting apparatusprovided by the present invention to fabricate semiconductors comprisesfabrication processes 601 to 609, defect inspecting apparatuses 610 to613, a probe inspection process 614 and a data analyzing system 613.

Having a big effect on or greatly affecting the yield, the fabricationprocesses 601, 605, 608 and 609 are monitored all the time by the defectinspecting apparatus 612 such as the one provided by the presentinvention. If an abnormality is detected between the fabricationprocesses 601 and 606 by this monitoring, the fabrication processes 602,603 and 604 are monitored by the defect inspecting apparatus 610 todetermine the abnormality or to identify the failing piece of equipment.The particularly important fabrication process 607 is monitoreddedicatedly by the defect inspecting apparatus 611.

By the way, in order to allow only a desired process to be inspected fora foreign particle or an outermost surface in the desired process to beinspected for a defect such as a foreign particle attached thereto witha high degree of precision, an inspection for a defect such as a foreignparticle is implemented by using the defect inspecting apparatus 612provided by the present invention before and after the desired processand, then, a result of the pre-process defect inspection is comparedwith a result of the post-process defect inspection to find a logicaldifference. In a judgment on the existence of a defect such as a foreignparticle based on the logical difference, a foreign particle generatedbefore the process must not be incorrectly interpreted as a defectintroduced during the process. A pre-process defect should rather beignored. This is because a pre-process defect leads to a measure toprevent a defect based on a wrong judgment.

By merely using the logical difference described above, however, it isnot always possible to detect only a defect such as a foreign particlegenerated in the process in question due to the following reasons.

For example, a film is created in a film formation process on a surfacehaving a defect such a foreign particle. Thus, the size of the defectsuch as a foreign particle increases, raising the inspectionsensitivity. As a result, a defect that has been existing since a timeprior to the film formation process is detected after the process. Thatis to say, the defect that has been existing since a time prior to thefilm formation process was not detected before the process but is foundafter the process and is incorrectly regarded as a defect generatedduring the process.

In order to solve this problem, in an inspection prior to the filmformation process, the multiplier m1 is typically reduced to decrease athreshold value and to increase the inspection sensitivity. In this way,a defect that has been existing since a time prior to the film formationprocess can be detected and an incorrect judgment can be avoided. If theinspection sensitivity prior to the film formation process is increasedas described above, however, the number of incorrect detection caseseach generating false information also increases. By computing a logicaldifference (B−A) between results obtained before and after a process asshown in FIG. 51, nevertheless, this problem can be solved.

However, conditions of a surface before and after a process may varyfrom area to area in a chip of the inspected substrate 1. For thisreason, even if threshold values are decreased entirely before theprocess, the background level increases. As a result, the thresholdvalues increase and there is introduced an area which is in fact in anuninspectable state or a low-sensitivity state. An infinitesimal defectexisting in an area in such a state can not be detected.

In order to solve the problem described above, the CPU 417 of thecentral processing unit 400 of the defect inspecting apparatus 612judges a defect to have been generated in a process P only if, forIb<Tb, Ia>Tha is detected and Ia>K×Thb. That is to say, a defect isjudged to have been generated during a process P only when no defect isdetected in an inspection prior to the process P even at a highestpossible inspection sensitivity but the defect is detected in aninspection after the process P even if the inspection sensitivity isreduced and the threshold value is increased. If no defect is detectedin an inspection after the process P when the inspection sensitivity isreduced and the threshold value is increased by K times, processing toignore defects is carried out to avoid an incorrect judgment, becausethe possibility in which a defect is judged to have been generatedduring the process P is reduced. Of course, if Ib≧Thb, the CPU can judgea defect to have been generated before the process P.

The symbol Ia denotes the level of a detection signal of a defectdetected in an inspection after the process P and the symbol Ib denotesthe level of a detection signal of a defect detected in an inspectionprior to the process P. The symbol Tha denotes the level of a thresholdvalue obtained from the threshold-value-map storage means 419 after theprocess P and the symbol Thb denotes the level of a threshold valueobtained from the threshold-value-map storage means 419 prior to theprocess Pat a lowest possible inspection. The symbol K denotes acoefficient which is greater than 1 and determined in accordance withThb. It should be noted that the comparison circuit 414 employed in theimage-signal processing unit 400 of the defect inspecting apparatuscompares Ia with Tha and Ib with Thb.

Thus, the aforementioned processing to form a judgment on the existenceof a defect such as a foreign particle carried out by the CPU 417 needsthreshold-value levels (a threshold-value image) of all chip areas orconforming areas prior to the process (in some cases, after the process)which have been obtained from the threshold-value-map storage means 419and stored in the storage unit 427. The CPU 417 also needsdefect-detection signals before and after the process which have alsobeen obtained from the memory 404 and stored in the storage unit 427.What is important here is the fact that information of a threshold-valuemap for inspections before a process is stored in the storage unit 427in advance and that the coefficient K is determined to be used indetermination of a threshold value (K×Tha) for an inspection after theprocess by using the information of the threshold-value map. As a matterof course, Tha is computed by the threshold-value computing means 418 inan inspection after the process.

The following description explains monitoring techniques adopted by thedefect inspecting apparatus 612 to monitor the fabrication processes602, 603 and 604. According to a first monitoring technique, attentionis paid to a particular wafer in a lot and the wafer is monitored forchanges in state of attachment of a defect such as a foreign particle tothe wafer every time the wafer goes through each or the processes.According to a second monitoring technique, attention is paid to aparticular piece of fabrication equipment or a particular fabricationprocess and, by monitoring the states of a wafer before and after theparticular process, the state of the particular piece of fabricationequipment or the particular fabrication process can be monitored. Apoint common to the two monitoring techniques is that the state of afabrication process is monitored. However, it is an object of the firstmonitoring technique to compare fabrication processes with each other,while it is an object of the second fabrication technique to comparechanges of a fabrication process with time with each other. That is tosay, it is an object of the second fabrication technique to monitor anaccident such as a sudden generation of a foreign particle or toevaluate an effect obtained as a result of implementation of somemeasures to reduce the number of defects such as foreign particles.

The defect inspecting apparatus 612, in particular, control to payattention to a specific fabrication process or a specific piece offabrication equipment for the process, allows the user to know how thenumber of defects generated in the process can be increased or reduced.In addition, from the size of a detected foreign particle, the controlparticularly determines the fatality of the inspected wafer caused bythe foreign particle in the fabrication process, hence, allowing theimportance of a measure taken for the foreign particle and a motive forimplementation of the measure to be known. The control is thus veryeffective. That is to say, by knowing the scale of an effect of ameasure taken for a defect such as a foreign particle, the user becomesmore strongly conscious of awareness of the measure, being led to anaction taken to implement the measure.

As described above, data obtained from the monitoring is supplied to thedata analyzing system 613 for analyzing, among other things, generationof an abnormality, its correlation with data received from the probeinspection process 614 and its correlation with the yield.

In addition, as the defect inspecting apparatuses 610, 611 and 612described above, defect inspecting apparatuses adopting optical brightvisual-field inspection and SEM inspection techniques can be employedbesides the defect inspecting apparatus provided by the presentinvention. These defect inspecting apparatuses have their owncharacteristics so that foreign particles that can be detected by theseapparatuses are different from each other. Thus, by combining thesedefect inspecting apparatuses, the total reliability of the defectinspection can be increased. In addition, these defect inspectingapparatuses have different inspection times or inspection throughputsdue to differences in detection principle. While the laser scatteringtechnique adopted by a defect inspecting system for a high throughput issuitable for inspection of an inspected object for an infinitesimalparticle, the complementation rate during the inspection is low due tolaser interference. On the other hand, while the optical brightvisual-field inspection technique has a high complementation rate, itsthroughput is low due to the fact that a high resolution is required ina sampling operation for comparison inspection. In the case of aninspection technique using an electron beam, it is difficult to increasethe inspection speed since the SN ratio is low. However, this techniqueis suitable for high-resolution inspection of an object for a defectsuch as a bad electrical conduction.

In an LSI fabrication process, systemization of these defect inspectingapparatuses is required along with a need for consideration of thesensitivity, the throughput and detectable objects.

By increasing the number of defects such as foreign particles that canbe detected by each of the defect inspecting apparatuses from a domain24 to a domain 27, from a domain 25 to a domain 28 and from a domain 26to a domain 29 as shown in FIG. 33, the total number of detection casesof the system can be raised. As a result, it is possible to construct asystem having a high performance as a whole.

FIG. 34 is a diagram showing a curve 30 representing changes in yieldwhich are obtained during a build-up time of a mass production. Thediagram also shows a curve 31 representing changes in detected-defectcount. As shown in the Figure, as the yield increases, the number ofdetected defects decreases. Even in a build-up state of the yield,however, the number of detected defects may increase all of a sudden,decreasing the yield. In such a case, the generation of the defects isrecognized quickly and production based on fabrication processes causingthe defects needs to be halted temporarily in order to determine acountermeasure for causes of the generation of the defects. That is whythe defect inspecting apparatus provided by the present invention isrequired.

As described above, according to the present invention, the efficiencyof illumination can be increased and the intensity of a diffractionlight generated by a pattern on a substrate such as an LSI pattern canbe reduced by using a spatial filter and adjusting the direction of theillumination. In addition, it is possible to decrease a threshold valueat each of positions on a chip with variations different from eachother. As a result, there is exhibited an effect of a capability ofinspecting a substrate such as an LSI wafer for a foreign particle or adefect existing on the substrate with a high degree of sensitivity at ahigh throughput.

In addition, according to the present invention, by using an ordinaryTDI image sensor with a high sensitivity, there is exhibited an effectof a capability of detecting an infinitesimal foreign particle and adefect existing on an inspected substrate, on which repetitive andnon-repetitive patterns coexist with each other, with a high degree ofsensitivity at a high speed.

1. An apparatus for detecting defects on a specimen, comprising: anillumination optical unit which obliquely projects a laser focused ontoa line on a surface of the specimen; a table unit which mounts thespecimen and which is movable; a detection optical unit which detectswith an image sensor an image of light formed by light reflected fromthe specimen and passed through a filter which blocks diffraction lightresulting from patterns formed on the specimen; a signal processor whichprocesses a signal outputted from the image sensor of the detectionoptical unit to extract defects of the specimen; and a display unitwhich displays information of defects extracted by the signal processor;wherein the filter is adjustable.
 2. A method for detecting defects on aspecimen, comprising the steps of: mounting a specimen on a table whichis movable; obliquely projecting a laser focused onto a line on asurface of the specimen; detecting an image sensor an image of lightformed by light reflected from the specimen and passed through anadjustable filter which blocks diffraction light resulting from patternsformed on the specimen; processing a signal outputted from the imagesensor to extract defects of the specimen; and displaying information ofdefects extracted by the signal processing.